Originally my plan was to buy an HDT. Based on reading this forum, escapees forum and other RV forums an HDT is the safest TV for heavier 5th Wheels.
The RV'ers who have had 3500/350 or 4500/450s and then switched to an HDT all said they would never go back. They sighted two major factors Safety and Ride Comfort both loaded and empty.
Since HDTs are designed to haul freight for at least a million trouble free miles a well kept used one with 300,000 up to 600,000 miles on it still has a lot of life left to give. You can get a nice used HDT for $25 to $40K and register it in most states as a motorhome with some additions like a sink, microwave and refrigerator in the sleepercab. You won't need a CDL if it's registered as a MH.
I went to test drive an HDT and realized my DW and 92 year old dad would never be able to climb up into one without the use of a lift of some sort.
I settled for my 2007 Chevy C4500 Kodiak dually crewcab which had been upfitted by Monroe Trucks. It makes towing our 15000 lb 5th wheel a dream. It feels so much safer than our previous C3500 dually crewcab. I no longer worry about going up or going down 6 to 10 % grades it tackles them like the trailer isn't there.
The turning radius on the MDT and HDT is much better than a 2500/250 or 3500/350. This helps with manuevering in tight campgrounds or camp spots.