[57taskforce]

Your model of truck will help a lot in narrowing this down. If it's a half ton it's likely a 12 bolt gm, but there are some light duty semi floating Dana 60s around. The gm will have 12 bolts holding the diff cover on. If it's a 3/4 ton it's likely an eaton ho 52 which is identifiable by a removable 3rd member. It could also be an hd Dana 60. Both will be full floating rears but only the eaton will have a removable 3rd member.
I don't know as much about the 1 tons but I do know they should have and ho72 which is mostly the same as the 52. I think the Dana 70 was a possibility as well but I'm not positive.
This is all speaking in Chevys. Gmcs primarily with the 3/4 ton trucks had Dana 60s.