writing this because i searched for something like it last winter and mostly found brochures. in march we traded a 2018 Freelander 31BH on the Chevy 4500 for a 2021 Jayco Seneca 37K on the Freightliner M2 106 with the Cummins 6.7. first full season is done, about 7,200 miles, Colorado and Utah, Yellowstone, the Black Hills in august.
fuel went from about 8 mpg on gas to 10 or 11 on diesel. diesel ran 60 to 80 cents a gallon higher most places, so it is closer to a wash than the salesman made it sound. the exhaust brake on the grades west of Denver is worth the trade by itself. coming down Vail Pass i touched the service brakes maybe twice. the ride is stiffer, my wife says it rides like a truck because it is one.
the catch: 37 feet and about 12 foot 6 tall. we lost a lot of Colorado state park loops and a couple of forest service campgrounds we used to love. and it has air brakes, so learn the air system even if your state does not ask for any endorsement.
on the plus side the weight ratings are big enough that we stopped thinking about weight. tows our Wrangler without noticing it. current Seneca specs are on jayco.com if you are curious how they compare to a regular C.