Everyone saying buy another truck and sell after fixing should just as well say trade trucks. GM will compensate dealer for trade, they have a recall running for this issue so dealer knows truck will get fixed at no cost to them. The dealer that told them to drive it home was likely right. The issue is spool leakage which is worse at higher tranmission temps.  What happens is tranmission skips a lot if gears on 8-7 downshift when the spool leakage is excess which results in temporaty rear wheel lockup since the transmission ends up in a much lower geare momentariy.  GM implemented software to detect leakage and derate transmission to max 5th gear to prevent wheel lockup issue from 8-7 downshift issue until vehicles are repaired; this allowed vehicles to remain useful while protecting agains the hazardous situatio of rear wheel lockup that results in loss of vehicle controler. The dealer has said okay to continue driving since software patch will prevent damage to transmission comonents.  Additionlaly, only when excessive leakage is detected will it go into limp mode and the software will trigger limp mode about 10,000 miles before wheel lockup will occurr.  Pretty sure it affects all GM 10spds.