Looking at a 93 half ton with a new venture 5 speed and new process 241d t-case swapped in. There's trouble in the case. If you park it in gear and rock the truck, the output shaft and yoke slide out almost a half inch, jumps a few splines or teeth or something, then pops back in.

Any ideas what's causing it?

Truck is a w150 with magnum 318. Looks rough with only 122 thousand on it.

 

Ouch, it aint good. Here is a cross section of the 241, looks like serious stuff if the output shaft is moving in and out.

The good thing is they are relatively cheap to buy.