I've been rebuilding transmissions for 26 yrs, and never ran into this problem.I reasonaly rebuilt a 4R/55E in a 2000 Ford Explorer put the trans back in the unit and the Transmission shifts excellent ,after you let it warm up as soon as the temp gauge hits the first line on the temp gauge about 5 minutes it works excellent ,but until it warms up it acts like it has a stall in it. If you just get in it and try to drive it will just rev i don't think its slipping just won't go until that temp gauge reads the on the first line then your gone,but you shut it off 10 to 20 minutes it does the stall again just revs then poof after 5 minutes.I thought maybe a defaulty torque converter but no deal. I have great hope in u FORD KINGS and the Oldtimer-if he ain't gone-fishing