Happens occasionally, some talk of it on the off road forums. Some have replaced the snap ring with "Gilly's T-case saver", do a google search...
It's a two piece collar that you cinch on the shaft with allen screws and replaces or eliminates the snap ring, supposed to be a better fix.
1994 K1500 Silverado ext cab short box
stock L56 6.5 TD, F intake, 4L80E, 3.73 gears
10149599 block, D-Tech PMD on 5288 pump
Goodyear Wrangler silent armour 265 75 R16 E Pro Grade
Bushwacker fender flares
410,000 km