A friend has a 2006 6.0 F250 Powerstroke. If you start it and drive off soon after starting, it moves fine. If you let it idle for 10 min or so, it won't move in any gear. If you shut it down and restart, it will move. It has 150K miles, trans has never been serviced. I'm going to replace both filters and do a few spill and fills and go from there...any ideas?