If all is well in the gears, then it does sound like your Hi torque motors are drawing more power than either the battery or control board can supply?

For example - I have a set of high rpm 380's here that will basically move the tank about 6" before shutting down the Tamiya DMD that they are hooked up to. I did some research on the model they were intend for and discovered that it comes with a 70A ESC(!) - the DMD can only supply about 20A before it shuts down.