2002 Eddie Bauer edition Ford explorer 4.6 V8 over revving
 

Ok so I have a 2002 Eddie Bauer Ford explorer. It has the 4.6 l V8 engine with automatic 4x4, 4x4 high and 4x4 low selective options. Transmission has been rebuilt, it does not slip, and I went to the Ford dealership to make sure the transmission fluid was topped off and perfect. My problem is when I am going on a flat surface or up a small hill or downhill, everything works fine. But when I start going up a steeper Hill, I have to press the gas in More but when it downshifts, IT red lines almost as if it popped into neutral and is not in gear. it has a new torque converter, new gears, new everything. Transmission was completely rebuilt with new parts. What could my problem be?

It is an automatic 5speed with overdrive

There have been instances when an addl pint of trans fluid into the trans helped get rid of the problem.