Recommendations for well built trailer

We really like our 21 foot Rockwood Minilite, which has a similar floor plan to what I saw for the Lance on their website. The dry weight of our trailer is about 3700 lbs, so likely close to 4500 fully loaded. We towed it for the first year with our 2011 Honda Pilot, which has the full tow package and transmission cooler, However, the Pilot strained pulling through the New England mountains -- did okay, but felt to be at its limits and could not hold the speed limit on the steeper hills. In addition, the towing mileage of 8 to 10 mpg gave us a pretty limited driving range with the 20 gallon tank. So when we planned a trip out through the Rocky Mountains, we purchased a Grand Cherokee diesel, which has worked wonderfully for this weight and length of trailer. We love the
Pilot, but felt that we were pushing its limits with a trailer the size that you are considering,