I see noone is placing their bets, other than 12V who thinks I need a built trans and a re-gear on the truck that ISN'T broken...lol.
So I'll provide an update.
Dealer says module(s) not the issue, replaced whatever modules and no fixey the issue.
Say its NOT the trans and it's engine related. Shcecked spark plugs and injectors and they're grrrreat! (I could have saved them that effort, lol)
Now they're heading into the innards of the engine! :( I'm not actually sad, but I will be if they turn a perfectly good engine into a leaky pos with issues by taking stuff apart that they can't put back together right)
Seems the known 5.3/6.2 lifter issue could be the culprit. Will see!