I have an '05 2500HD, that weighs over #7,000 without the TC. I have Lance 2004 Lance 1025 model (10'3") and have easily 10G miles on it. After I load it up with provisions/toys etc., put it on the scales and it weighs in at #13,000+. I have been on bad roads, and heavy winds, and the firestone airbags work great. I have OEM Brand new take offs (3rd set) that I buy off of craigslist, and have a total of 95K miles since new.
The front wheel bearings ($500+ Dealership item) that I replaced myself ($195.00) at 70K miles. That is usual it seems. The wiring to the lights is my only gripe, and a constant pain.
As far as being lucky, I don't see it that way. Load and Balance is the key here folks! And Heat destroys parts. I have all stock parts too, no aftermarket so called performance products! ( I have, but took out my Edge W/ attitude, as it lowered my mileage! ) Everything runs cool, and I might someday buy a set of 5 Ricksons 19.5 Rubber, as I see that is the weakest link! But, even the tires so far have run cool enough! Those tires add even more weight, but it is unsprung weight. Mine is SRW, and owned DRW and it can't find a decent parking spot!!!
I use a digital Infrared Guage to check brakes, Bearings and the Third member, usually every stop for safety. I don't get complacent, and check air pressure as well, at least every other stop. I carry SCUBA gear ( 2 full sets ) which isn't light, but I have an adapter to use tank air for filling up to 80 PSI, period! 50 PSI goes into the firestone's with separate schraders, mounted on the forward bottom lip of the right (Pass) side rear wheel well.
I get 12 + - MPG loaded, I drive 55 mostly! And up to 21 MPG hwy with bare bed or Leer Cap and Heavy Pipe Rack!
Whew! Said about all of it there....any questions?