I'll add my two cents worth. We've only had one trailer and one tow vehicle but we full timed around North America three times over three years plus a few years of traveling to Florida. The trailer has about 85,000 km. on it and the truck about 185,000 km. The truck is a 2013 Ram
1500 with the tow package (including the 3.92 rear end and 5.7 litre hemi) and the trailer is a 28 ft. International. We've had no drama over the years, it just works. I drive at about 60 mph on highways as that is the speed where I feel comfortable (the few times I've exceeded that speed, the truck/trailer combination handled fine). We haven't had any problems with 6 or 7% grades, as for anything steeper, that's what the Mountain Directory is for.
We have weighed the truck/trailer and found it somewhat overloaded - but the axles were well within spec. The truck came with load range E tires so no problem there. If I were to buy a new truck, I might look at the F-150 which I believe has a larger payload or possibly the Nissan. The hitch is an Eaz-Lift with additional anti-sway bars and was set up by Can-Am RV.
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