sometimes it gets hot like when your pullin a trailer and will jump out...other times its the overdrive solenoid(sp?) thats goin to crap..which at worst could be an early sign that your tranny is crappin out on you. when i bought my dodge it was like that, good for 15 miles or so then it would jump out of o/d, i ended up gettin a rebuilt tranny put it..at the dealers expense of course 
