Is a GMC truck just a dressed up Chevy truck?

The 3.8?

They did pretty much put that in everything, but I've not seen one in a firebird or camaro.

Those cars did get the 4.3 (but I think not until the gen 4 body), which was actually a pretty good engine for those and other smaller cars and even the s-10.
Funny the s-10 got that engine way earlier IIRC.

Wait, maybe I did see a camaro with a 3.8 once. Almost bought it for my mom.