With the Chevy Duramax, 05 or newer, the 04 and older have injector problems. 06 and newer have the 6 speed Allison the 05 a 5 speed; I have a 05 with 160,000, has never been in the shop, Went to change the shocks and brakes about 5 thousand miles ago, shocks needed replaced, probably 50,000 miles ago, brake pads were still like new (original pads). We pull a stock trailer and a travel trailer, plus the wife drives it to work, if you run at around 2000 rpms it get around 19 MPG empty and 15 MPG pulling. No chip no aftermarket products, just change the oil and fuel filter regularly, run injector cleaner every few tanks. The Allison Transmission is the best part of the Chevy, plus the fact after driving 5 hours straight in it, I can walk. After 3 in the ford I feel like I just played 4 quarters of football.
Most the of the Ford people I know are going to either Chevy or Dodge when it comes to Diesel, we used to run Fords at our shop, but the newer ones spend more time at the dealer then in the field. Our shop truck a flatbed has been in the shop 5 times it has 100,000 miles on it and the last visit it came back terminal, blown number 8, $13,000 for the motor, not counting labor.
I think if you could put the Allison with the Cummings, get the Chevy comfort in the Ford body, you would have quite a truck.