Take a careful look at the shift linkage. Strange problems can occur if the linkage gets whacked by road debris and it leaves you finding something other than the correct positions. You might even try, as I would, removing the linkage and, with a trusted helper, shifting it into gear right at the transmission with the engine running, wheels chocked, parking brake set, and brake pedal mashed down with both feet. Make darn sure that your helper is perfectly trustworthy if he or she is in the driver's seat for the test, and that nothing that doesn't need killing today is under the truck when the pressure on the brake pedal is released.

If it's not funky linkage... Bang is not a noise automatic transmissions are supposed to make and it's always very bad news when one does. If the "something like a dry wheel bearing" and the "bang" both came from the transmission, chances are good that no measurements were taken during the rebuild and you've now got broken hard parts and maybe a ruined case.