This is a topic that is of great interest to me because we tow a smallish trailer with an 05 4 runner v6, 2wd.
I'm posting because I need to increase my number of postings and because I'd like input on our experience and expectations.
We plan on taking our 4r and camping trailer to a scale on Monday to get a base line. To weigh the combination: the trailer will not have water, because we don't travel long distances with water, but it will have everything we keep in it for camping. bbq, dry food, pots and pans...stuff like that. it will have battery and full propane tank. the 4 runner will have full tank of gas, but not much more. We usually have a couple of telescopes, a kayak on top and two smallish dogs, but I'll just take it solo to the scales.
some formulas I've based our decision on is the "20% less than rated rule" and the distance from trailer axle to hitch point should be no more than twice the wheel base of the tow vehicle. our trailer at 3750# GVWR is under 20% less than the 5000# tow limit. 2X the wheel base is 219.6" and our new trailer is 173" from axle to hitch, so we are within those guidelines too.
I don't see anywhere that toyota gives frontal area restrictions, but our new trailer is the same width and height as or old one, just longer. We towed the old one effortlessly, and so far, can tow the new one with ease.
We haven't driven the new trailer much, but have driven up some pretty long and steep grades, and some wind. based on how it towed, I would say it will be fine. we drive in the mountains, and we have some very windy days in NM, and have realistic expectations. As I mentioned, we don't expect to cruise along at 75, we are going camping in the mountains with a trailer. we are retired and like to go midweek to have the places to ourselves.
As far as downshifting, that's normal to expect, I would think. My son has a ford truck well suited to towing a heavy load, and his truck downshifts going up big hills.
so that's my 2 cents, for what it's worth.