Transmission Problems!?!?!

I have a 1994 GMC sierra Z71
5.7L V-8 I purchased back in Dec of 02. I drove it with no problems
until I deployed over seas in Feb. of 03. It sat until I came home in Sept.
and didn't have any problems with it till Jan. 04 the U joints went bad
so I replaced the rear joints and couldn't get to the forward joints in time before the t-case cracked just behind the pan and in front of the
t- mount so I took it to a shop to be looked at and replaced they replaced the case but couldn't figure out why it cracked in the first place so I took it home and two weeks later the same thing they replaced the case for free because it was still under warranty but said they would not do it again and still didn't know why it was cracking so once again I take it home and this time a week later it cracks only worse this time and noone seems to know why this is happening.
and I cannot afford to keep replacing cases only to have them break again a week later. The forward u-joints still havn't been replaced but I'm reassured that that wouldn't have anything to do with it. This all happened in a 2 month period between Jan and Mar and its now July and me and my wife are trying to figure out what to do with the truck its been sitting since Mar.

I do go out and start the engine every now and again.
I would like to keep it.

Any Help in this matter would be greatly appreciated by many including
myself.

Thanks !

Kerry

Did you happen to mark the driveshaft to make sure you put it back together the same way as it was before(yoke to yoke, not 180 degrees off)? If you didn't you may have some driveline vibration that MAY have caused your problem.