Just had a van body truck come in with a 5.9 cummins and an allison automatic, engine codes were erratic signal from both engine speed sensor and vehicle speed sensor. I checked the wiring from each sensor everything good, did ohms on sensors good. I took the truck out for a ride and the check trans light came on and the vehicle would not shift from 2nd. Ran diag on trans and found signals not working properly when going through gears. Next I checked the wiring at the shift switches on the side of the trany, low and behold when I unplugged the lower plug 2 wires had rubbed through near the plug on the backside. repaired the connection and everything cleared. I guess my point is even with codes it sometimes only gives some direction and not the answer.