[rickst29]

My 4Runner "Sport" is the direct predecessor of today's "TRD off-road" models. It tows great on going up and down mountain passes with a heavily loaded 2619 (I have 5000 lb suspension, like a model 3124.)

But you can't leave the transmission to make it's own decisions when driving on hills. It will tend to stay in 5th, or 4th, lugging along at low RPMs when you NEED to hand-shift it down by another gear. (To 4th or 3rd, or even 2nd, raising the RPMs to provide enough power.) On CA-120, from the Nevada side, I have also used "low". But that road has crazy grades, well above 20% in a few places.

The "cruise control" in my 4runner is also wonky, frequently jumping by two gears (into excess RPMs) both with and without the Trailer. I only use it on long, flat straightaways, with very limited nearby traffic. (In Nevada, we have a LOT of roads where it fits. But hills into and down from mountain passes are absolutely no-no from cruise control.

The V6 engine/tranny combination which 'oldstick' and I share was a 4.0L engine, with slightly more displacement than newer models ones. My engine likes 2800-3800 RPMs on stepper hills, while the Auto-Tranny often lets it fall into the range of 2100-2400. Newer models (I've driven a few) can rev a bit higher on steep hills, and have different shifting logic, but the overall situation is roughly the same - they prefer to "lug" then engine at lower RPMs to save gas, when you should be running higher RPMs to have more power.

Higher RPMs can allow the Tranny to "lock" and reduce RPMs. (It can do this in all gears 3-5, and maybe 1-2 as well) This helps to "win back" gas mileage being spent by higher RPMs, but much more more important - it keep tranny fluid from sloshing around between unlocked clutch plates, working too hard and overheating. The biggest danger in "lugging" Tacomas and 4Runners in low gears is overheated transmission fluid.