I tow my 21ft boat with my 5th gen 4runner (which is probably right at the weight limit), but it is normally only a handful of times per season for a few miles (I keep the boat on a lift in the water). When I initially bought the boat, I towed it ~100miles on the highway, which was sketchy as the trailer brakes didn't work. I have since rebuilt the brakes and it tows well enough for my needs.

I have rented uhaul auto transports many times to tow my 1959 MGA behind my 4runner (both my 5th gen, and my previous 3rd gen), which weighs about 2000lbs. As noted, the uhaul trailer is really heavy, but with the light weight of my MG I was likely still under the 5000lb limit. I've towed several hundred miles in this setup, and it worked fine, however the uhaul trailers are poorly maintained and I highly doubt the brakes really work (in my experience lots of banging and clanking from the trailer when accelerating and stopping). My boat trailer is completely quiet when underway.

Good luck, and if you go this route, go slow, leave lots of room to stop, etc.

Jim

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In addition to weight dist. hitch, ensure tire pressures are good all around. Reduced rolling resistance goes a long way for several areas.

Could get SumoSprings for the rear instead of air bags. Both assistance with towing and a progressive bumpstop if you go off road. If you do go off road I'd get the blue model, and if not then the black if you're going to tow a lot.

Had the opposite surge brake experience as Jetboy.

Hauled this in our last trip escaping commiefornia.
It was really loaded and I was really careful with weight distribution inside.

Went over the Siskiyiu range no problem. Just can’t be afraid of RPM’s.
The UHaul surge brakes surprised me and worked very well! But my last experience with them was many years ago when they were downright terrifying.

My 4Runner may as well be in natural down hill, so the UHaul brakes were really nice for me as it did braking downhill while not accelerating. (My wife’s SR5 had much better engine braking.)

I think the 4Runner is capable of doing what you want. But the real question is if you should, as it sounds like you easily become overloaded.

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I came across an interesting YouTube video today, comparing air bags to a weight distribution hitch.
The Difference Between Using Weight Distribution and Air Bags to Level Your Load - YouTube

Air bags are a crutch.