@hdhp We have a 2016 Ram 2500 with diesel and ran a ~1600 pound Northstar TC650 popup on it for for 4 years. The truck has been great, but I think the rear coil suspension on the Ram 2500's is a really bad match for a slide-in camper. The coils are mounted inboard of the frame rails causing a lot of sway with high center of gravity loads. The rear track bar also causes some goofy tail-wagging-the-dog effects.
Even though the camper load is not all that heavy or tall for a 3/4 truck, I've needed to add Timbrens and a Hellwig sway bar to correct sway issues.
With the Cummins, G56 trans, and 35" tires we get 14-15 MPG running around Colorado when loaded up.
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