If you go new the Lance 855s is what I would recommend for your truck. Plan on adding a set of Supersprings ($450) to add to the load capacity of your truck. The tires may also be a problem as the factory ones are likely to have 3195 lb load capacity and that will limit your trucks overall payload.
Take your truck to a CAT scale and weigh it to get the weight at the drive wheels and subtract that from the total max load for your truck's two rear tires. That difference is the maximum load you can put in the bed, which includes the camper, water, food, gear, toys, etc.
The very good thing is that your truck has a very solid frame and even the factory shocks are good ones. No need to do anything more than the SuperSprings and possibly the tires.
A new camper will likely cost you almost double the cost for a comparable one that is 3 years old. Part of it is depreciation and part of it is that new campers keep going up in price.
You can download brochures for prior years from the Lance website and this is very helpful in seeing what models will work for you and for your truck and this makes shopping for a used on much easier. For example the Lance 830 and 845 short bed models were excellent designs in many respects but they were discontinued. You can get a used 830 or 845 camper in excellent condition for a third of what you will pay for a new 855s camper.