The Gospel of Thomas doesn't really overlap with the synoptic gospels. What passages do you think are related?
The Gospel of Thomas is just a collection of sayings, and there are tons of overlap between the Canonical gospels and Thomas. Q is also believed to have been a collection of the sayings of Jesus. Here are some teachings in Thomas that are similar to the Canon:
GoT 9- Jesus said, "Look, the sower went out, took a handful (of seeds), and scattered (them). Some fell on the road, and the birds came and gathered them. Others fell on rock, and they didn't take root in the soil and didn't produce heads of grain. Others fell on thorns, and they choked the seeds and worms ate them. And others fell on good soil, and it produced a good crop: it yielded sixty per measure and one hundred twenty per measure."
GoT 16 -Jesus said, "Perhaps people think that I have come to cast peace upon the world. They do not know that I have come to cast conflicts upon the earth: fire, sword, war.
For there will be five in a house: there'll be three against two and two against three, father against son and son against father, and they will stand alone."
GoT 20 -The disciples said to Jesus, "Tell us what Heaven's kingdom is like."
He said to them, "It's like a mustard seed, the smallest of all seeds, but when it falls on prepared soil, it produces a large plant and becomes a shelter for birds of the sky."
There are other parallels, but for the sake space here, I suggest to anyone that they should read the Gospel of Thomas. Some parts of it are weird, and others good. Q would have probably been much the same way if it existed or continues to exist.