Do chimps and gorillas ever interbreed?
Nope. There is more of a difference, between a chimp and a gorilla, than there is between a chimp and a human.
Also, they don’t find each other attractive. 
There is no known instance of chimps and gorillas interbreeding in the wild or in captivity. However, note that the relative genetic distance between chimps and humans vs chimps and gorillas has little to do with that.
Chimps live in very different kinds of social groups than do gorillas, and both animals are very territorial.