low12lightning

Having trouble with my truck today. Attempting to dyno the truck and have the issue that transmission is stuck in safe mode. Truck wants to start in third gear and will do nothing other than stay in third gear due to the confusion in the PCM. Truck Idles at 10 mph in Park and Neutral, however will drop to zero when idled in all loaded gears. Have gone as far as to unplug VSS sensor and still idles at 10 MPH. Appears as if some sort of RFI interference is happening. Wondering if anyone here has seen something similar? Read some threads about alternator feedback, however have tested and no similar traits exist... Someone must have seen this before???