dodge 3500 frame

I hauled a similar sized and weight Fleetwood (maybe bigger, it was a 12 1/2ft model) with my '1991 F250 for 20 years. Hauled my family of 6 and towed a 21ft offshore fishing boat behind it a lot of the time. The frame flexed a lot but never broke. I did put a piece of stiff foam between the cabover and the cab roof to reduce bouncing and it seemed to help.

Bottom line, I would have expected much more from your truck. I am sorry to hear about your problems. I have heard of frame issues with the diesel in earlier Dodges but thought that it had been fixed by 2009.