You figure this out? Having the same problem I think.
C0268 (motor stalled) on a 2005 Silverado 1500HD I just purchased. Had ABS light with above code and C0226 (left front speed sensor signal missing). ABS was not working Cleaned the grounds and the speed sensor code went away and can now feel the brakes working much better in the pedal and hear the pump. The C0268 comes back immediately on takeoff no matter how many times I clear the code.