Transmission drag oil pan

My son is having a problem with his 1996 Jeep Grand Cherokee 4.0L with 42re trans.
Jeep has 3/4 ton axles Dana 60 in front, 10.5 Sterling in back with 40 inch tall tires and home built custom 3 link suspension front and rear.
Every time he tries to climb a steep incline he will lose the transmission(feels like it kicks into neutral), get back to level ground trans works perfect again.
We figure that all of the fluid is running back into the overdrive unit and away from the pickup.
That trans pan would probably cure the problem, but he would most likely tear it off while rock crawling, got to come up with some kind of baffle in the pan to keep the pickup submerged on steep forward climbs. His last Jeep Cherokee a 2001 4.0L with the Asian Warner trans and 37 inch tires didn't have this problem.