My MD70 seems to sometime loose all drive power to both tracks. If im pushing into a dirt pile or up a steeper grade sometimes I just loose most of the forward drive power. The tracks will try to slowly go forward but with very minimal power. The engine does not bog down at all. Normally I just reverse which works fine and then go forward and all is good. Today I was on the edge of a very steep hill and I lost reverse drive power. I could go forward fine, just didnt really want to. Turned the engine off and on, no difference. Dropped the grapple into the ground and spun the tracks forward fine. Just couldnt get any reverse power. Eventually I got enough to get away from the clff and then all drive power came back. I am wondering if this could be a relief valve popping open and sticking. When driving most of the time I can load up the engine when pushing slowly. This seems to be more if I load up the tracks more suddenly. Sometimes Forward or reverse I just loose power, put the controls to neutral and then slowly give it drive power and it works fine. The problem does seem to be getting slowly worse. I am going to soon have the tank open to change out the bucket hydraulic pump and am looking at what to check in there on the drive pump.