Here's my real world experience:
We bought a 38FT 5th wheel 13,000lb weight.
Truck 1-At the time I had a Chevy 3/4 ton 4X4 with a 350 engine. The tow rating was 10,000lb for a 5th wheel.
I towed the trailer once with the 350 and decided I needed a bigger engine. So I had a 454 built and installed. This worked OK but the truck didn't have enough brakes to safely stop the trailer.
Truck 2- I bought a used 1 ton Chevy with a 454 v8. Towing was a lot safer and the truck would slowly climb 6 to 8% grades but going down a long 6% grade got scary. I would begin to run out of brakes by the time I reached the bottom of a 10 to 20 mile down grade. Even in first gear.
Truck 3- My current truck is a 2007 C4500 Chevy with the Duramax engine and allison transmission. It is equipped with an exhaust brake. This is the right truck for towing our 5th wheel.
The only caution I have regarding a medium duty truck (MDT) like mine and the FL60 is the ride. These trucks when empty ride rough. The RV'ers using Heavy Duty Trucks (HDT) all indicate the ride of their HDTs is much more comfortable than the MDT many of them had prior to moving up to an HDT.
The only reason I didn't go to an HDT is my wife and 90 year old Dad would not have been able to safely climb up into the cab.
By the way my MDT has the exact same measurements (width & length) my 1 ton pickup had. So I'm comfortable using it as a daily driver.