Both of the GM SUVs that our family has had (11 Suburban and 18 Escalade) have both had what GM calls "auto-trac" 4x4. You have your normal settings (2hi, 4hi, and 4lo) but you also have 4auto, where the car is AWD. Its RWD until it detects slip, then it engages 4wd. I'm pretty sure this was also on SUVs of the Roamer's age. Another thing that they both have had is a G80 automatic rear locker. When one wheel exceeds 180rpm of the other wheel, the differential locks (not a limited slip) and stays locked for 5 seconds, or until wheel slip has stopped. This would be nice to see in-game.
