UPDATE: I figured it out. I installed the Hot Racing adjustable motor plate. It fit perfectly, same thickness....but for some reason it causes the slipper and shaft to bind in some place. So the friction is the extra "brake". I re-installed the original plate and it drives like the devil now...
I'm wracking my brain. I replaced the motor plate with the hot racing one. Then re-installed everything. Now when I drive there seems to be a 100% brake applied. The takeoff hesitates (like it's fighting a brake at low speed) and any time I let off the gas, it locks up and spins out. It should...