Transmission disengaging on a steep hill

My 2nd gen tacoma crawler will disengage on a steep hill (40 degree), roll back two feet and then catch and reengage. This all is at low RPM or idle. ATF is full, Fuel Full. Any Ideas??

 

the 1st thing im lookin at is the Inclination

at 40degrees fluid is probably running away from a ' pickup ' or ' pooling '

where it aint doin U no good

no less at that inclination crankcase sump oil might be running away from the oil pickup

to the engine

at idle neither trans / engine is pumping much & not a lot o pressure

' any ideas ' ???????

thats my 2cents

good luck