Agree with Grit dog. A 1-ton GM truck only has a larger rear differential and an extra set of springs compared to the 3/4 ton truck with the gas engine. With the diesel engine the only difference is the extra leaf pack. For under $500 you can add SuperSprings and accomplish the same thing.
I found ten 2500HD trucks on dealers lots within 400 miles from my house for every 3500HD and the 1-ton pickups all were either regular or crew cab models. I wanted the shorter wheelbase with the extended cab. If you don't mind paying extra with a special order truck and want a crew cab anyway then the 1-ton may not cost that much more. But even if it cost an extra $1500 I would look at the net cost of paying an extra $1000 and go the Supersprings route instead.
The important aspect of any truck you get is the wheels and tires provided as they are what will limit the rear load capacity. My stock rear tires would carry up to 6400 lbs. and minus the weight of the truck that left 3200 lbs. for the camper, fully loaded, water in the tanks, etc. and that was not enough.
I replaced the stock tires with ones that provided at the rear and extra 1100 lbs. of load capacity using the factory rims. Others have gone to 19.5 wheels and tires but with the new GM 8x180 bolt pattern on 2011 and later pickups that is a problem and I could only find the overpriced Rickman steel wheels at $400 a wheel.
With a SRW truck I would go with a camper that had a dry weight of less than 3,000 lbs. and with the awareness that whatever the published weight is from Lance or anyone else is minus a lot of things like a battery (or two which is an option with the 855), roof rack, AC, TV, and that the true dry weight is probably going to be 400 lbs. greater than even the sticker weight on the rear of the camper.
If I had a choice between a camper like the Lance with its TPO roof and one with a fiberglass roof, with all else more or less comparable, I would go with the fiberglass roof. There is one manufacturer that makes a two part molded fiberglass camper that in theory should be exceptionally weather tight but in reality is more prone to letting water inside.
Check the exterior height of the different campers. Some are a 10-12 inches greater than the Lance at 86" and I would not want the extra height and worries about clearance with tree branches or the extra air drag driving down the highway.