I wonder if anyone who thinks these 1-ton trucks can't handle big loads have every even towed with a 1-ton.
Why does everyone think they can't stop big loads? Obviously you people don't realize that the TRAILER does the braking and not the TRUCK. With the trailer properly setup, the trailer brakes actually help slow the truck as well before the truck brakes even connect. When I have my dump trailer or camper hooked up, I can actually stop sooner and easier. It's easier on the truck brakes since they are being helped by the trailer brakes. Trust me, when the brakes hook up on a tri-axle goose neck, it will haul that trailer and truck to a stop immediately. The truck doesn't even need brakes with proper trailer brakes.
Today's 1-ton trucks would run circles around older class 5/6 trucks and YES they can get used commercially day in/day out. Plus it's a TON cheaper to maintain. Ever price out some 19.5 or 22.5 truck tires? How about a brake job or even an oil change?
I have towed a fair bit with a new 1-ton (2010 dodge 3500 cab chassis, 6.7L 6spd) and while I agree they are leaps and bounds above the 1-ton trucks of 20 years ago, they still do not compare to a 2-ton truck.
They are great for a 10, 12, 15K trailer, but once you start getting towards 20K you can tell its a real load. I've used the aforementioned dodge to haul our 2550 JD + disc mower a few times, gross trailer weight about 19K. Even with all that torque you still slowed down to about 35mph on the big hills, not to mention had a hard time starting out at a steep stoplight due to a lack of deep gearing (and very little low end torque until the turbo spools up). And heaven forbid the electric trailer brake plug comes undone on one of the 7 mile long 9% grades we have around here. BTDT, very nearly wrecked, not fun.
Compare that to our old '75 C60. It is pretty slow and a gas hog, but it hauls that much without issue. It too slows down to about 20mph on the hills, but with a deep first gear and an 8.85:1 axle ratio on the low side it's no trouble to get a load moving. And, while it may have drum brakes all around they can easily stop 20K WITHOUT any trailer brakes (although I wouldn't make a habit of it.) For long hauls I would want something more modern and comfortable, but for short hauls there's absolutely nothing wrong with it.
Maintenance costs? With a 350 gas motor and SM465 trans you can get parts at almost any auto parts store in the country. Brakes can still be done for a reasonable cost using parts that most NAPA's still stock. 9.00-20 or 10.00-20 tires while not common these days are available and much cheaper than 19.5 or 22.5 tires. Sure it gets about 6mpg, but you can buy awful lot of fuel for the $50K sticker on a new truck.
Having used lots of different truck and trailer combinations, no one will ever convince me that a 1-ton pickup is a better tow vehicle than a 2-ton truck when you get into the 20K range.