Oh, it's one of those FineDesign jobs. You might want to try something. If you can, put a 3S lipo pack on it or just the nimh equivalent and see what happens.

I know that a few of his setups, especially those meant for buggies, are "designed" to be run on 3S rather than 4S. It might just be a really high kv motor and you have it way overgeared.