Well my first thought was why in the heck are you running a 308 gear and 38 inch tires? That's a heck of a torque load on the drive train. I would drop the gear ratio a BUNCH. That will help.
Then on your second post, if I read you right, you've taken the slip yoke and welded it solid on your rear driveshaft?
You are either A) breaking the housing from the torque load of very tall gears with large tires, or B) you are beating the driveshaft into the transfer case hard enough to break off the trans ears when the rear suspension flexes over uneven ground.
The definition of insanity is repeating the same steps and expecting different results.
I'd be making some changes to your setup.