Bummer on the cracked tranny case. I looked at the pictures but didn't see one of the tranny torque converter cover installed. Did you use the aluminum cover for a 4x4 with the steel support rods that go to the motor mounts? Also, iirc, the 4x4 700r4s have a stronger case with a K cast into the right side bellhousing. Was the case that broke a K case?
Another thing to check for is if the front driveshaft is bottoming and trying to rip the trans off the motor.
(some GMs have a rod going from a bellhousing bolt to the front driveshaft side of the tcase to help with the driveshaft thrust loads.)