Corrections to the above posts. The GMC is likely to have a Spicer 45, not a dana 44. I can't tell you what the diference is, but they are different. Very few dana 44 parts will interchange with the spicer 45. If the jimmy has a spicer, it is possible it also has posi, as that was an option. The only con to this rear end is the brake drums can be difficult to find if they are bad. It should match up pretty well in an AD chevy