heres some bad news the problem u r having i have had twice and is the bg problem w 700r4 but can be cured unfortunatly u need a tranny rebuild and when you tell them to rebuild it tell them to put in a slight stall converter with a shift kit for towing and put a tranny cooler on it if not already and no more prblems ever but if it slips in over drive and not in drive the fourth gear clutches are worn out