I would say it is a shift solenoid sticking.I have not had a problem with my Jeep but I have a 95 Nissan Altima that goes into limp mode(stuck in 2nd gear) if I spin the tires in the winter time.After I turn the key off and restart again it is good to go again until the next time the tires break loose.It has done this for the last 50,000 miles and still runs and drives just fine as long as it is getting traction.Hardly ever happen in the summer unless I hit a mud hole or something.I doubt you see any mud on the interstate but its an idea.