'16 was the first year for 8sp behind 6.2. '15 had the 6L80 behind the 6.2. More preferable. All 5.3 had 6L80. I assume you will get a 6.2 after driving mine.
708 is a internal mode switch. very rare for them to go out. 722 code is speed sensor code. No way to check TCM except to put a known good one on and see if problem goes away.
They do not feel at all like the G3. Their lining is hard as a rock and the pattern will trap fluid which is a no no. That lining was meant for slow moving trucks. No good for the shock apply we do under high TQ.