Nordictrack A2050

I have been working on this treadmill for a bit. Symptoms are: surges when it starts up before settling into the speed. The speed step buttons do not work as set. 1 mph is actually 1.6, 2 mph is actually 3.5 as shown on the display. Have replaced the circuit card in the bottom of the treadmill 3 times, with the same results. Cannot complete a calibration as the speed at setting 85 is over 15 mph and cannot be adjusted down. The belt will slow down when stepping onto the treadmill. I can actually stop the belt by dragging my foot, ie, no torque. The belt moves freely when the power is off and I walk on the treadmill. I checked all connections between the control panel circuit card and the motor control card. I adjusted the speed sensor closer to the magnet as it was over 1/4" away. no change. Owner took the motor into a local electrical shop and had the brushes replaced.

Thoughts or ideas as to what to look at?

Thanks
Dave