We currently have a 2020 OR and previously had a 2012 SR5. We have towed a 5000lb Boat / Trailer combo for years. Disclaimers.
We try to tow @ 65 MPH or less when off highway. We have never towed more than 400 miles in a single run. Load is balanced and relatively streamlined. We live in Florida, so hills are a non-issue. We have disk brakes on all 4 trailer tires, and trailer is well maintained. In 7+ years of towing that load, no issue of any sort. No overheating, no instability. 2 flat tires, 1 on truck, one on trailer, both uneventful. Average MPG with this load about 11 MPG. Tires are KO2 255/75’s. Suspension is standard. Trailer tongue weight just shy of 400 lbs. Slight rear sag when towing, but not too bad. Prior to this setup, we have decades of experience towing much heavier loads with much bigger trucks.
Based on our experience our 4runner meets our current towing needs. If we were towing a boxy trailer, higher tongue weight, mountains, huge tires or extra heavy modified 4runner, the results probably would not be as decent.
Thanks so much for writing this out! Calculating the weights, i think i'd come in at ~5,400lbs. Do you think that'd extra 400 pounds will make a huge difference? Are flat tires a more common thing while towing?