turns off in revers

just did a engine and transmition swap on a 93 jeep grand cherokee , reson for swaping was because the engine wold rattle after about 30 min. now everything runs fine. exept for the facted that when i shit into revers it wants to die. what could it be? it drives fine in all the other gears expet for revers. just dies. when you first turn on the car its fine it will shift after about 5 min if i want to shift in revers it dies unless i flool it but still almost dies. can any one help ?