Thanks for the reply Cpt.
On the Bench with the wheels off the ground, it accelerates and brakes fine.
Seems normal.
I've tested the diff tightness. I hold the spur and right tire while checking to see if the left wheel will slip. It barely slips. I tightened down just a little.
When I do a quick test - it would run ok if started slow and gradually speed up. But when you just blip the throttle it would slip.
I've adjusted the slipper to almost full lock and does the same.
I will try to go to the track today and do more testing.
After you eliminate the other possibilities check to make sure your rotor is not slipping on the motor shaft. Take it out and mark the rotor/shaft with a sharpie then see if the marks move after running.