We got one of the first ones and learned some things before trading it in on a 2500. It's an outstanding light truck: powerful, smooth, quiet, comfortable, drives well and is indeed economical for a pickup. We easily got 25 MPG unloaded, less when towing a travel trailer but still good (18+ MPG). Best results for us on a tank was around 28 MPG hand calculated. Some users have gotten over 30 MPG. Of course, fuel economy depends on many factors such as speed, terrain, driving style, load, tire pressure, etc. Air temperature, fuel mix and trip distance also have a major effect on diesel economy.
We had air suspension which was awesome for towing and general use. Not so good for payload because it stopped working when the load exceeded roughly 800 lbs over GVWR. The stock coil suspension can be beefed up--sacrificing some ride quality--but payload is still a limiting factor because of the light duty axles (3900 GAWR) and the heavy diesel engine with emissions equipment. The most popular model is a crew cab which will have a rated payload of roughly 900 to 1200 lbs depending on typical options, so pushing the GVWR is necessary to carry even the lightest of slide-in campers. At least one person on another forum mounted a Lance 825 (2000 lbs dry!) on a Quad Cab with only better tires and Timbrens and they claimed that it drove and stopped fine. Other owners have installed an Outfitter Caribou Lite or a Four Wheel Camper Hawk on a mid-level Quad Cab with satisfactory results. For most people a basic standard cab with coil suspension would give more payload leeway and should handle a light pop-up plus a passenger and gear.