3126 cat shuts off while driveing

2000 Gmc c6500 3126 cat Allison transmission. I'm having problems with it shutting off while driveing. It will restart but once you starting driving again it shuts back off. Re starts. It's got me puzzled. I replaced the heui pump, fule filters, ipr, injector harness, pulled all the injectors looking for bad o rings. Replaced the fuel pressure valve. On the back of the head. Still shuts down while driveing. Runs all day long as long as its parked. I'm not able to get a scan tool to hook up to the computer. I dont know if its because the person I bought this truck from changed the steering column. If any one can help I would really appreciate it. Thanks..