You are both right. The original concern was not having sufficient power to climb a grade at speeds above 40 mph. That scenario requires max hp for the engine. That point occurs at 5600 rpm at wide open throttle, so that's where you want to be. 

When cruising down the freeway at 60 mph, our rigs use only about 45-50 hp. Engines can develop that at an infinite combination of throttle and rpm settings. In reality of course you are limited by gearing to several options. Of those, the one that keeps the rpm the lowest will be the most efficient because that reduces pumping losses.  Since hp= torque x rpm/5252 (in US units) there won't be an issue of undue stress on the engine due to torque requirements because the hp requirement is low. You'd have to be down around 1000 rpm before that became a problem. If you're around 2000 or so your engine should be pretty happy and your fuel economy should be good. 

In my young and stupid days, I towed a ~2800 lb boat with a 2400 lb, 100 HP Datsun and it would do better.  Are you limiting RPM manually? 

Originally posted by mjlrpod I have a question on this. I tow a 195, so about the same weight. I try to keep it about 3500, but under 4000 r.p.m. when climbing. I just think it sounds like it's working hard at 4000 or so. The tach starts to red line after 6000 r.p.m.. So is it ok to run as much as 4500 - 4800 r.p.m. even though it "sounds" rough?? I know it's kinda hard to really know, just wondering if occasional higher r.p.m.'s is ok for climbing.

After the engine and trans are fully warmed up, the green zone is idle to redline.  Use it.  200 HP at 3500 RPM is 300 lb-ft.  200 HP at 6000 RPM is 175 lb-ft.  Which stresses your frame and trans most?  Both yield the same climbing speed.  Perhaps high RPM "sounds" hard on the engine, but it's not.  Oil and coolant flow are proportional to RPM.  My sports car cruises between 3500 and 4000 at legal speeds.  Both of my bikes redline over 10k.  Even the Duc wakes up over 6k.  So, I'm used to it. 

Sure, it should be fine to run at the higher rpm occasionally, just noisy. If the manufacturer didn't want you to ever run at that rpm they would have set the red line lower. 

Given the choice, I prefer to run at a higher rpm in a lower gear to develop the same hp and speed when climbing grades in hot weather. The cooling system works better at higher rpm. That is less important these days with electric radiator fans but it used to make a huge difference in engine temp with belt driven fans And boy did it make a big difference in old air cooled VW's. It would be the difference between having a burned exhaust valve or not by the time I got to the top of the I5 Grapevine in CA (ask me how I know). 

We need to separate weight carrying capacity from engine torque and power. Two completely different things. The WWII deuce and a half trucks that one us the war could carry and haul many tons with only 100 hp. They just went slow. 

So, the issue you are describing is lack of power climbing grades. That would be a horsepower issue (not torque). Your 4Runner max HP is 270 at 5600 rpm. Not sure what gear you're climbing in abnd what rpm you're seeing but see if you can select a gear that gives you around 5000-5600 rpm. Still not fast enough for you? You'll need a TV with a higher HP rating. 

Back on weight handling for safe towing. I agree that a 192 is pushing the max limits of a 4Runner. I suggest you weigh your trailer  and rig as set up for travel and be sure you are under the max trailer weight, max tongue weight, and max combined gross vehicle weight of the 4Runner. You can do the weighing at a public scale, if you search on the forum I wrote up the procedure I use. 

 

My tow vehicle is an Xterra, 261hp/281lb-ft and I don't have any problem towing my 180, but I guess it's quite a bit lighter.

Going up steep grades on the highway to the mountains I max out at about 40MPH.

I'm considering getting the Ford Ranger - max tow 7500, torque 310.

Is that enough to not be so sluggish on a steep highway grade? 

Do I really need to step up and get something like an F150 with 400 lb-ft torque?