My guess is that your spacer still isn't allowing enough airflow. You might do well to look into machining grooves for ventilation into the CIM-U-Lator plates. There's a thread addressing this. We've posted CAD drawings of our modifications.
http://www.chiefdelphi.com/forums/sh...ight=cimulator
I can't think of any other reason, unless maybe your motors are opposing each other, although I'd think that if that were the case it would have been caught ealier.