I don't know if it's still the case but . . .
With GM, it used to be that if you got the 6.0 gas engine in a 2500 it had a 10.5" rear axle. If you got the diesel in a 2500 it had the 11.5" rear axle. If you bought a 3500 it had the 11.5" regardless of engine. So, the the case of a gas GM truck, yes, a 3500 does get you a stronger axle.
OP, get the 1 ton. Anyone considering a TC should regard a 1 ton SRW as MINIMUM. If you want a fancy hard side camper with slides I'd look hard at a dually. You'll probably be overweight no matter what you buy so try to minimize the problem. I'm 2,000 pounds over weight on my dually and my camper doesn't even have slides.