Keep in mind medium duty trucks are designed for fleet service. The expected life is 500,000 miles. So a truck with 100,000 miles is just getting broken in. Heavy Duty Trucks (HDT) are designed for a million miles of service.
In 2007 when I started looking for a MDT to tow with new M2 sportchassis were $120,000. The C4500 Kodiak Monroe conversion that I bought new had a sticker price of $105,000. Luckily diesel prices were approaching $5.00 per gallon so I was able to negotiate down to $80,000. At that time you could find an HDT with 300,000 miles that had been setup to tow an RV for less than $50,000
After towing with the Kodiak C4500 I would find it very difficult to go back to a 3500. The C4500 is so much more stable and safe feeling than my C3500 was.
The folks who have gone from an MDT to an HDT say towing with the HDT is way more comfortable than with the MDT. I had to go with an MDT because my 90 year old Dad and my DW would not have been able to climb up into the cab.
