EDIT: Acutally now that I re-read the original post, I actually started to solder the battery backwards. Took it off and re-soldered it the right way, but too late. But it was acting like yours sounds like it is. Pull the trigger and just kinda grunts. Wheels turned great just didnt have any foward movement to it.
Mine was a Futaba MC800c
It was a real good speed control, just my stupidity burned it up.