That's a contradiction in terms. Truth is absolute by definition.

Gnosticism is based on the principle that there is an absolute truth.

A fundamental mistake the pythagoreans (and other greek schools) made was mistaking mathematics for truth, but nonetheless they knew what truth was and they were searching for it. Part of the reason they liked mathematics is because of how absolute it is. They did spend some time discussing other subjects such as aesthetics but mostly they were focussed on things that could be proven true or false.

This was not something they suddenly came up with in the first century AD, it was a behavioural trend they'd been following for millenia.

Also, as I pointed out to hump, there's Zoroastrianism. An entire indo-european religion dedicated to truth as the highest good and lies as the deepest evil.