I have a 2015 35sk so its similar, this model has the small slides which are much less of an issue. I'd be concerned about the full-wall slide on the 35sf which also has a lot of power, water and gas lines sliding around with it, where as the 35sk nothing of importance is on a slide which was my main reason of mine for choosing this one. If you go with the 35SF verify it atleast has the slightly better triple rail shwintek slide system.
As far as power and towing, I live in the mountains and can still do 60 on the long 6-7% grades around here, while my friends in their class A's are down to 40 or 50. I tow our Bronco on a car trailer which is around 8k lbs or our rzr on the same trailer for around 4k lbs and you know its back there but its not a huge concern for accelerating or braking.
I've had no cap issues, I think its primarily on the 19+ omni/magnitude models that have major cap issues, vs the older 13-18 front cap.
EDIT:
Oh and just so you know the power is no where close to your pickup if that's what you're expecting. Its spiffy for a giant box on wheels but the chassis cabs are only 300hp and 660 ft lbs, mated to a 6 speed. Your pickup has 475hp and 1050tq to a 10 speed.
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