The consensus is not that it's Gnostic and hasn't been for nearly two decades now. Here is Princeton's Elaine Pagels (author of Gnostic Gospels) on the topic in a recent email debate:

Both of your points are assumptions all of us, I would guess, were taught in graduate school. The earliest editors of "Gnostic" texts thought that they were dualistic, escapist, nihilistic, involving "esoteric ideas about aeons and demiurges," as you yourself write. As my former teacher at Harvard, Krister Stendhal, said to me recently about these texts, "we just thought these were weird." But can you point to any evidence of such "esoteric ideas" in Thomas? Anything about "aeons and demiurges"?

Those first editors, not finding such evidence, assumed that this just goes to show how sneaky heretics are-they do not say what they mean. So when they found no evidence for such nihilism or dualism-on the contrary, the Gospel of Thomas speaks continually of God as the One good "Father of all"-they just read these into the text. Some scholars, usually those not very familiar with these sources, still do.

So first let's talk about "Gnosticism"-and what I used to (but no longer) call "Gnostic Gospels." I have to take responsibility for part of the misunderstanding. Having been taught that these texts were "Gnostic," I just accepted it, and even coined the term "Gnostic gospels," which became the title of my book.

I agree with you that we have no evidence for what we call "Gnosticism" from the first century, and have learned from our colleagues that what we thought about "Gnosticism" has virtually nothing to do with a text like the Gospel of Thomas-or, for that matter, with the New Testament Gospel of John which our teachers said also showed "Gnostic influences."

• Source

It used to be what scholars thought, but it's one of the big recent instances in Biblical scholarship of "oops, our bad" and is now definitely an obsolete position, particularly by anyone specializing in Gnostic studies.

As for Paul's use of it, I'm not saying he was reading it prior to his conversion, simply that he's likely read it or become familiar with it by the time he's writing 1 Cor given the overlaps, which given their nuances indicate that the core text was present in Corinth when he's writing to them. I suspect it is the "other gospel/other version of Jesus" he's chiding them for accepting in 2 Cor 11, as well as what was behind the schism in Corinth that 1 Clement was written in response to. So it's not necessarily influencing Paul 2-3 years after the crucifixion, but more around 50 CE shortly before he's writing those letters.

And there's unique sayings or context in Thomas that fit parts going back all the way to the time of a historical Jesus.

For example, saying 81 doesn't only parallel 1 Cor 4:8, it especially fits Pilate's time because it was then that Tiberius, who inherited the throne, had abandoned ruling to party but didn't relinquish the position to someone else. So "let someone who has become wealthy reign, and one who has power relinquish it" sounds a lot like a critique of dynastic rule and a call for Tiberius to pass the torch to someone that will do the job. It also sounds like the kind of thing that might have gotten someone killed by the Roman state.

Or the context of Leucretius as a foundation, present across Thomas, happens to fit one of the most well known parables. Look at Leucretius's language in describing failed biological reproduction:

For a woman prevents pregnancy this way, resisting it, [...] By doing this, she turns the furrow away from the straight and true Path of the ploughshare, and the seed falls by the wayside too.

• De Rerum Natura book 4 lines 1269-1273

The book elsewhere explicitly described the idea that only what survived to reproduce would multiply.

So you have the sower parable about randomly scattered seed that fails to reproduce when it falls by the wayside of a path, and only what successfully reproduces multiples. The Naassenes, following Thomas, claimed this parable was referring to the scattering of seeds like indivisible points that make up all things (almost verbatim Lucretius's "seeds of things"). In Thomas, it immediately followed two sayings about how no matter if lion ate man or man ate lion humans would be the eventual result, and that the human being was like a large fish selected from smaller fish.

Yet in canon the saying is given a secret explanation about proselytizing. One that in Mark clumsily interpolates into a public speech at the shore (you'll notice they never return to the shore after 4:20, but are back there in 4:35-36).

So one version of the tradition around what's regarded as one of the most likely sayings to go back to a historical Jesus effectively has Jesus citing Leucretius's metaphor in describing survival of the fittest, and the only other version from antiquity is instead saying that he explained this public saying in secret (at odds with John 18:20's "I said nothing in secret") and it was about proselytizing.

In parallel to this, you can see that Paul is first talking about sown seeds in relation to human bodies in 1 Cor 15:35-49 where he also discussed a first and second Adam (a core aspect of the later Naassenes' beliefs), but then switched to discussing sown seeds in relation to proselytizing and collections in 2 Cor 9:6-10. (Here's a paper exploring Epicurean influence on the opposition to the physical resurrection in 1 Cor 15, btw.)

Is all of Thomas dating early? No - there's even evidence that parts of Thomas post-date other parts of it, such as 110 combining the adjacent 80 and 81. But there's a case that parts of it go back much further than most people might think (in part because of terrible scholarship for about 50 years leading to misinformation regarding it).