I can't find the information to decode a rear I bought. I was told it was a Trans Am Rear from 79.
The code is 4 PR G 3331
Can someone help with this so I can get some parts for it.

I tried that PR code on the Trans Am site, and I didn't come up with anything. I can't find a PR code at all for Firebird or Camaro. Are you sure it is PR and not P(something else)?

Maybe someone else has a more complete listing somewhere.

Your best option is to pull the cover and find out what ratio the rear end is.

As long as it is a GM 8.5 inch rearend, and that is all the 79 Trans Am could get, you can get parts for it just knowing that much. The ratio can be easily found out by the numbers on the ring gear when you get it opened up.