The '82 to '89 GM trucks had the 8.5 10 bolt with 28 spline axles. In '90 they upgraded to 30 spline axles. The rear end didn't change other than that. In '98 GM upgraded this rear end again to a 8.6 inch ring gear and they increased the differential bearing size to 3.062, the same as the 12 bolt. The reason for the bearing size increase was because when they increased the axle size in '90 they had to bore the hole in the differential case larger, which made the bearing journal too thin. They started having problmes with the left bearing breaking off of the differential case. If you want to increase the strength of the whole rear end then look for a '98 or later complete rear end. Many of the trucks in these years had 3.73 gears in them. Look for RPO code GT4 on the sticker inside the glove box. As far as I know all of the '98 and later rear ends had disc brakes too.
The problem with the GM truck rear ends is that the only limited slip differential that they used was the Governor Lock (Gov Bomb), which is not a good differential for high performance use. The Eaton Posi is a much better differential, but you have to buy it new and install it. Tom's Differentials is a great place to get the Eaton Posi.
