A few years ago I was looking to replace my F350 Dually IDI with a powerstroke. Was using craigslist. Not finding what I wanted. Typed in F550 in search and up came the holy grail. F550 with Pick up bed. It is a MDT. Engine and Trans same as the F350 but rear end is a Dana 135 front disc 14.5 in and rears 15.5 in.
!9.5 in tires. It's a beast.
If you have a bucket of cash a newer F450 6.7 is rated to tow in the area of 33K lbs. A beast.
There are also 650's out there with pick up beds just biger than I wanted to go.