All things considered, it did okay. I towed exclusively in S4 to keep the OD off, but I might as well have only had a 2 or 3 speed tranny anyway. Headed up to camp, I really did not find myself out of second gear most of the time due to speed, incline, and again, lack of low end power. Ute Pass out of the Springs is not steep by CO standards, but the winding road keeps the speeds down enough that I could not get out of second without losing all my power (RPM) and momentum. There are a few decent hills beyond the Pass as well, and any time I hit the slightest of inclines chugging along in third gear in the 50-60 mph range, the vehicle speed would start to drop steadily and you could tell the vehicle needed to be in a lower gear, so I would then drop the speed sub-50 mph and drop it to second gear to find some power again, which was in the 3k-4k RPM range. Getting the speed up to 60+ mph in third gear to find the power was a challenge on this stretch of Hwy 24. This was a short trip, 1/1.5 hour to our destination, but I could seriously see this getting old on a trip across state or lengthy road trip. I just don’t like the RPM revving so high for a long sustained period, which limits top speed. Coming home was no problem as it is mostly flat or down hill, so I finally was able to find and use fourth gear again.
So, it gets the job done, but is a little annoying having to be so limited. I might consider regearing to 4.56s just to give me another usable gear option/shift point, but will probably spend the summer on stock gears to see how some more challenging routes/grades go; we are headed to Estes Park for July 4th and down to the Sand Dunes NP in August. I am concerned, too, about regearing and losing a good usable speed/RPM/power zone---power in second gear in the mid-40 mph zone is ideal and critical for many passes we frequent, not the least of which I am concerned about is Monarch. I might wait for one of our trips to Ouray before I make the final decision on regearing for towing as I do not want to find myself in between final drive ratios/speeds with the sweet spot somewhere in the middle.
Anyways, hope that helps. For anybody finding themselves in the OP conundrum, searching for a trailer to tow in the mountains with their 4Runner, do yourself a favor and keep the weight down to a 3500# max. I cannot imagine trying to pull anything heavier.
Good report. As far as what to do next, I think you just have to weigh your tradeoffs. I used to pull my 2500# pop-up from Loveland (north of Denver) to Ouray down highway 285 and across Monarch pass with my '94 3.0 V6. Probably about the same power to weight ratio as you have with your 4.0V6 and a 3500# trailer. Yes, it definitely took some time to get over Monarch - about 30 minutes of uphill at 4000 rpm in 2nd gear doing 40mph, but the little 3.0 just ate that up. Never showed any signs of distress. At the time I also owned a '99 Suburban that would have towed that popup without even noticing it, but then I would have been in Ouray driving the backroads in a Suburban instead of the 4runner - not at all ideal. So, it was worth putting up with an extra 15-20 minutes of travel time getting there to have the vehicle I wanted once I was there. It doesn't really add that much time to the trip - it just seems that way on some of the hills.
I do agree that 3500 lbs or so is probably about the practical limit to tow regularly through the Rockies with a 4th or 5th gen V6 4runner. Leave the 5-6000 lb rolling hotels for the guys with the long wheel base F250 diesels.