Well, let me try to use the proper terms here to the best of my recollection. I had trouble with mine once but not like this. My problem was a stick got into my Potentiometer and knocked it outta whack.....my tractor just flat quit like a clutch totally went out....I couldn't even get it to move......took it to the dealer and all they did was adjust the Potentiometer to the correct voltage. The Potentiometer is the little electrical thingy bopper right under your drivers side that the inching pedal is hooked to. It's easy to adjust, if I remember correctly you losen a screw and just turn it but it's having the correct electrical equipment that might be a trick.
Not sure if this is your problem or not, sorry I can't remember more exact on all of this but it sounds to me like you may be having something that's affecting the current coming from it......might check and see if everything under there is free and not restricted or might have been bent or something.
Please keep us informed on your solution to this problem.......I may be having the same any day.