Need ally gurus!

[57taskforce]

Ladies and Gentlemen I need help with an 02 k/2500hd 8.1/Allison CCLB.188,000 miles.trans was rebuilt at some point in the past by a po. Mileage on this trans is unknown. It's my father in laws truck. Here's what's going on. The fluid is clean and red I changed it mid July last summer not even 10,000 miles ago. I did a rebuild on the transfer case late August as well due to a blowed up input bearing.(bearings, seals, shift forks,etc.) last week it threw a P0776 and went into limp. He limped it home and I used my scanner to clear the codes. Took it for a drive it shifted fine thru all the gears but I only drove it gently on acceleration as I read that P0776 could wipe 4th gear under certain conditions. No harsh shifting or slipping of any kind. Any ideas?