As to your title question, MN27 - http://www.accesstoinsight.org/tipitaka/mn/mn.027.than.html gives an account how every achievement before Nibbana, is no thing more than a clue as to the accuracy of the Buddha's insight. Prior to the attainment of arahantship, 'Truth' is not to be realised.
Practicing the same thing over and over again does make the mind 'run in that context' even outside of intentionally concentrating on that subject - I used to dream about weiqi when I used to play 4 hours a day.. In this respect, some aspect of Buddhist literature may be interpreted as only psychological (monks meditating and reaching the Tusita heaven etc.. Though these states are only ever acknowledged as psychological within Buddhism).
The difficulty with your point is that, if you skip annihalationism (nihilism), and embrace mundane 'right view', or:
"And what is the right view with effluents, siding with merit,
resulting in acquisitions? 'There is what is given, what is offered,
what is sacrificed. There are fruits & results of good & bad actions.
There is this world & the next world. There is mother & father. There
are spontaneously reborn beings; there are contemplatives & brahmans
who, faring rightly & practicing rightly, proclaim this world & the
next after having directly known & realized it for themselves.' This
is the right view with effluents, siding with merit, resulting in
acquisitions." - MN117
'truth' becomes evident. And if there are 'good and bad actions', there is a path that can skip the bad and keep to the good ones (assuming beings capable of discerning between the two). Would it then be reasonable to define 'Truth', having established 'truth', and a Path towards it?
From my reading of the Suttas, the Buddha did not pursue the concept of Truth. For one, in the Potthapada Sutta, the Buddha talks about 'exclusively happy states', which is how an Absolute state of Happiness (a Christian heaven?) would have to manifest (http://www.accesstoinsight.org/tipitaka/dn/dn.09.0.than.html):
"There are some brahmans & contemplatives with a doctrine & view like
this: 'After death, the self is exclusively happy and free from
disease.' I approached them and asked them, 'Is it true that you have
a doctrine & view like this: "After death, the self is exclusively
happy and free from disease"?' When asked this, they replied, 'Yes.'
So I asked them, 'But do you dwell having known or seen an exclusively
happy world?' When asked this, they said, 'No.' So I asked them, 'But
have you ever been aware of a self exclusively happy for a day or a
night, or for half a day or half a night?' When asked this, they said,
'No.' So I asked them, 'But do you know that "This is the path, this
is the practice for the realization of an exclusively happy world"?'
When asked this, they said, 'No.' So I asked them, 'But have you heard
the voices of devas reborn in an exclusively happy world, saying,
"Practice well, my dears. Practice straightforwardly, my dears, for
the realization of an exclusively happy world, because it was through
such a practice that we ourselves have been reborn in an exclusively
happy world"?' When asked this, they said, 'No.'
"So what do you think, Potthapada — when this is the case, don't the
words of those brahmans & contemplatives turn out to be unconvincing?"
"Yes, lord. When this is the case, the words of those brahmans &
contemplatives turn out to be unconvincing."
"Potthapada, it's as if a man were to say, 'I'm in love with the most
beautiful woman in this country,' and other people were to say to him,
'Well, my good man, this most beautiful woman in this country with
whom you are in love: do you know if she's of the warrior caste, the
priestly caste, the merchant caste, or the laborer caste?' and, when
asked this, he would say, 'No.' Then they would say to him, 'Well
then, do you know her name or clan name? Whether she's tall, short, or
of medium height? Whether she's dark, fair, or ruddy-skinned? Do you
know what village or town or city she's from?' When asked this, he
would say, 'No.' Then they would say to him, 'So you've never known or
seen the woman you're in love with?' When asked this, he would say,
'Yes.'
"So what do you think, Potthapada — when this is the case, don't the
words of that man turn out to be unconvincing?"
"Yes, lord..."
"In the same way, there are some brahmans & contemplatives with a
doctrine & view like this: 'After death, the self is exclusively happy
and free from disease.'... Don't the words of those brahmans &
contemplatives turn out to be unconvincing?"
"Yes, lord..."
"Potthapada, it's as if a man at a crossroads were to build a
staircase for ascending to a palace, and other people were to say to
him, 'Well, my good man, this palace for which you are building a
staircase: do you know whether it's east, west, north, or south of
here? Whether it's high, low, or in between?' and, when asked this, he
would say, 'No.' Then they would say to him, 'So you don't know or see
the palace for which you are building a staircase?' When asked this,
he would say, 'Yes.'
"So what do you think, Potthapada — when this is the case, don't the
words of that man turn out to be unconvincing?"
"Yes, lord..."
"In the same way, there are some brahmans & contemplatives with a
doctrine & view like this: 'After death, the self is exclusively happy
and free from disease.'... Don't the words of those brahmans &
contemplatives turn out to be unconvincing?"
"Yes, lord. When this is the case, the words of those brahmans &
contemplatives turn out to be unconvincing."
, whilst Absolutes are not Absolutely denied by the Buddha, given the empirical evidence of impermanence (and the non-self that follows), the only place where such Absolutes could be found is beyond empirical evidence - beyond experience (or Metaphysics, 'after Physics' - as Aristotle stated, with regards to the investigation of 'things' beyond evidence). As such, this Essentialist Truth - whether theistic or nihilistic - is only ever an inferred Truth - never a directly perceived Truth.. Plato's Parmeneides says as much!
".......... Then the one does not exist in such way as to be one; for if it were
and partook of being, it would already be; but if the argument is to
be trusted, the one neither is nor is one?
True. But that which is not admits of no attribute or relation? Of
course not. Then there is no name, nor expression, nor perception,
nor opinion, nor knowledge of it?
Clearly not. Then it is neither named, nor expressed, nor opined, nor
known, nor does anything that is perceive it.
So we must infer. But can all this be true about the one? I think
not.
Suppose, now, that we return once more to the original hypothesis....."
(Plato gets to the same understanding that Truth must be placed beyond all perception, if it Is. But he chooses to stick with the inferred argument, rather than follow perception)
The Buddha's insight however, is to be fulfilled at its end, with perception alone, as demanded by the Kalama Sutta (http://www.accesstoinsight.org/tipitaka/an/an03/an03.065.than.html):
"Of course you are uncertain, Kalamas. Of course you are in doubt.
When there are reasons for doubt, uncertainty is born. So in this
case, Kalamas, don't go by reports, by legends, by traditions, by
scripture, by logical conjecture, by inference, by analogies, by
agreement through pondering views, by probability, or by the thought,
'This contemplative is our teacher.' When you know for yourselves
that, 'These qualities are unskillful; these qualities are
blameworthy; these qualities are criticized by the wise; these
qualities, when adopted & carried out, lead to harm & to suffering' —
then you should abandon them."
and as fulfilled by all that become Arahats, as did Sariputta, helpfully described by the Buddha in the Anupada Sutta (http://www.accesstoinsight.org/tipitaka/mn/mn.111.than.html).
In his first sermon (http://www.accesstoinsight.org/tipitaka/sn/sn56/sn56.011.than.html) the Buddha stated the Four Noble Truths (http://www.accesstoinsight.org/ptf/dhamma/sacca/). These Truths are no thing more than declarative statements as to how the world is perceived to be. In a world that has Absolute constructs, the 'Truth' that 'all conditioned experience is suffering', is simply false. But no such world is either perceived to manifests empirically, or can be created within though without creating contradictions (for this read Nagarjuna's 'Fundamental Wisdom of the Middle Way').
The Buddha does link stress/suffering to impermanence and non-self within the Truths, and at this juncture you can definitely argue that psychology will play a part, as stress and suffering are psychological experiences, but you would have to find a mind that prefers constant change (and this includes death and rebirth) to certainty to argue that the Truths fail within the empirical world.