My previous truck (98. 5 2500 4x4) had 100,000 when I traded it in - no problems with the transmission at all, but it was also stock.
My new 02 2500 4x4 had 8k miles before the transmission went to pieces, after light (300HP) power mods. Now I have around 525HP, just turning 45,000 miles on the odo. I put an ATS Stage IV transmission and TC in when the stock one blew at 8k miles, and have not had a lick of trouble since.
HTH
-joel