Update:

We drove home yesterday and the wind was blowing slightly harder out of the north; still a heavy cross/head wind (15 to 20 mph).

This time around, I turned off cruise control and drove through the hills for the hour. During the inclines, I'd squeeze the gas just enough to get the torque converter to unlock in 5th. It was plenty of extra torque multiplication to go up all but a couple of the steeper hills which required a downshift into 4th.

I completely understand that the headwind definitely isn't helping here at all and is contributing to the issue. My frustration is that Toyota's shift logic while in cruise control almost always bypasses 5th gear TC unlock goes directly for the downshift. Why? It seems so simple a fix on their end. There are all sorts of sensors and vacuum systems that can help the ECU determine when to unlock the TC and when to downshift. Clearly the ECU has no issues when the driver is in full control and everything operates the way it should for a 2020 year vehicle.

I knew of the complaints of gear hunting with 4runners/Tacoma, but my God, I had no idea it was this bad. I rented tons of cars, trucks, and SUVs because of my job. I've rented and drove all across this country. I've never driven a vehicle with such poor shift logic.

This gear hunting issue is only compounded by the TRD Pro exhaust my wife really wanted. The downshift into 4th puts the exhaust right in the drone range of 3,000rpms under load. I wasn't for the exhaust because of my prior experience with exhausts on V6s and long geared automatics but it's her truck. She doesn't mind the sound even when droning up the hills, but I do feel bad for my kids in the back seat. I keep the stock exhaust boxed up in the basement with hopes she'll change her mind at some point

I do have concerns about taking the 4runner across KS into CO. Lots of cross winds and elevation change (800' in Kansas City to 4,800' at the KS west border).

I love the truck, but damn, there are definitely compromises (more so than I imagined). I have a feeling I'll need to drive without cruise in these situations.

It's too bad Toyota couldn't figure out a way to fit the 6AT from the Tundra or the 8AT from the Lexus vehicles into this truck. I don't think the power is lacking. The issue is lack of gears and shift logic.

It's a heavy, un-aerodynamic vehicle with a 4 liter V6. Regardless of the number of gears in the transmission, the transmission will always try to be in the highest gear on the highway for fuel economy. That means the RPM will be low, where the engine just isn't making enough power to handle grades, or headwinds, without downshifting to bring the RPM up to where the engine does make enough power to maintain speed.

That's why a Supercharger allows the transmission to stay in overdrive more often, despite grades, or headwinds. With the Supercharger, the engine makes enough power at low RPM to maintain speed in overdrive.

It is what it is.

Using your transmission as a brake going downhill actually causes your transmission to wear out faster.

Oh nah. That's just volume control for the traction control.

My problem with the shift logic is how quickly the car upshifts when getting up to speed during a highway merge. I continue to press the throttle but the 4runner just upshifts to 3rd or 4th gear, taking the engine right out of the power band. Shifting to "S" works slightly better, but the same behavior can be observed.

How? The compression of the motor is doing much of the work and there's not much load on the transmission as the motor isn't creating any power (injectors are turned off under engine braking).

Engine braking is a preferred way to control downhill speed because if you ride the brakes for a long duration of time, you may be met with brake fade when you really need them.

You do wear down the clutches a little more than normal. I usually blip the throttle half a second or so after downshifting so that the engine speed doesn't have to be brought up.

The extra torque multiplication of additional gears would keep the motor from having to work so hard and consume fuel like it does. A well geared 6+ speed auto and direct fuel injection would improve mpgs of the 4runner 20%+ and improve acceleration as well. It would also help find a better gear ratio on inclines and keep from increasing rpms by over 1,000rpms on a single gear downshift.

Toyota is ultra conservative and runs their models into the ground before making a drivetrain change. That is especially the case with their trucks. The only thing that really keeps them in the game is their reliability, especially with the Tacoma and 4runner. It is certainly not their drivetrain performance or amenities.

I love the simplicity and reliability of the 4runner, but damn, they could have updated the drivetrain at least once between 2010 and now and made their trucks even more desirable and competitive. Everyone, and I mean everyone, updates their drivetrains every 3 to 5 years.

FWIW my 2nd gen Tacoma (2011) had the same issue. But if you think that's bad, throw a camping trailer behind it, LOL. Had a time going to Yellowstone with it where I was trying to maintain a reasonable speed on the highway (55-60 mph) in Montana into a stiff headwind and instead of bouncing between 4th and 5th, it was bouncing between 2nd and 3rd! The sound was horrendous and it felt like I was killing the dang thing. After that trip I traded it in on a 5.0 V8 F150 which towed light years better.

Very good explanation by @Charles Bronson in post #26

The reason they update every 5 yrs is because they keep having warranty work on them, and they can’t keep them on the road. This is just me, but i have no problem with this tranny, i shift when i need to and enjoy the probability that my trans. Is going to get me home.

I most definitely agree with this. "If it ain't broke, don't fix it," can only be used for so long. 10 years maintaining the same powertrain in an industry where technology is advancing so quickly across the entire board amongst manufactures is not going to cut it. Ye,t I purchased a 2021 4Runner and have the same complaint as OP. so LOL.

My transmission consistently hunts between 4th and 5th ESPCIALLY when I'm using the adaptive cruise control and the incline grade slightly changes.

Does anyone know if there's a way to use the cruise control without it being dynamic and adjusting speed/distance? I just want an old school locked speed cruise control..

True, more gears means the potential for a better ratio for any given situation.

However, my point was that if the 5 speed auto and a 10 speed auto have the same overall ratio in their highest gear, and the same engine providing the power, both will downshift to get the engine RPM up to where the engine can maintain speed on a grade, against a headwind, higher speeds, or all of the above.

We have several grossly overpowered vehicles that can maintain speed in top gear on any highway. They are lots of fun for what they are.

The 4Runner is not overpowered, and makes due with it's 5 speed A750F transmission. Why I have it is because it's a great 4wd trail vehicle, and it's track record of reliability.

I have owned 3 4Runners, an 04 V8 4wd, 14 v6 4wd and 17v6 4wd, al three acted as discribed on the highway in hilly country i.e. always hunting between 4th an5th and not wanting to shift back to 5th when they should. That said, not sure if new 4 Runners work like my wifes 19 Highlander v6 but with it if you hold in the cc button in for 5 seconds magically you are in reg old cruise control not The assisted kind that brakes for you or keeps a constant distance relative to the car in front of you, maybe this helps maybe not.

All very true. It's basically like a hammer. Simple and effective. The 4runner, Tacoma, and Land Cruiser have a reputation to keep and when you're in the middle of nowhere on the trails, these are the trucks you want for sure.