This is the scan tool I use and I love it, plugs in under the dash and then connects to your phone via Bluetooth. There’s probably 100 different gauges to choose from but these are the ones that I use.
I was out west in March and this thing is a life saver; climbing trails you can get all your temps at a glance.

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This is the only warning I’ve got related to my transmission, ironically this came up right after I hit the summit of a trail out west in Northern Arizona. It came up on my navigation screen with only 37k miles on my rig, no warning lights.

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Second (or third or whatever) the trans cooler. I was regularly exceeding 230F in 4H up steep inclines until I put in a cooler, since I added it I haven't seen it exceed 190F even with very hard driving on hot days. It rarely gets above 170F and even when it does it drops pretty quickly once the load on the trans isn't so high.

Remember, Bishop is already at 4K feet. So you're likely higher. Your most likely issues (As mentioned) are that 1) you were in D (so lower RPMs, more slip) and 2) using 4H. Use 4L next time and shift the gears "manually" so you can keep the RPMs higher.

I've spent a lot of time in the hills of Bishop and lever had issues...

I mean if you wanna roll around at high RPM and murder your range then sure. I haven't been in that area but I've spent quite a lot of time on forest roads where 4L is just gonna make your fuel consumption awful or needlessly add hours to a trip. My thought is that if the suspension can handle the speed, the trans better be able to as well. Cooler was the definitely best option for my driving style and the areas I frequent, zero regrets. The hardest part of the install was working around all my other mods.

Going through the mountains and switchbacks at Bishop I upgraded to a Derale tranny cooler. Best thing I ever did for the transmission. Temps never saw more the 195 degrees in ambient temperatures of mid 90s. Seeing the temps steady in my Scanguage prove the money spent was worth it.

The transmission cooler:

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Before I had this i had to keep it in 4L to keep the temps down.

My setup:

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Probably not the worst idea to change that cooked fluid sooner than later.

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Once again — this forum does not disappoint. Thank you all so much for your kind insights.

The general consensus has been that there is no oil temp or oil pressure sensor, for that matter, in the 4R…at least no sensor that can deliver data to the OBDII. Is this incorrect?

I’m getting a good reading on oil temps with the unit I use. Not sure the location of the sensor but I assume it’s post oil cooler.

I can not find a 5th generation engine oil temperature sensor. I searched on Camelback Toyota using the terms "temperature sensor" and "engine oil temperature sensor". I also searched with Google "5th generation 4runner engine oil temperature sensor" and didn't find anything.

Your OBDLink MX+ is showing engine oil temperature 177.8 F which is too low if the engine is fully warmed up. Oil temperature leaving the engine and entering a cooler should be above 212, ideally 220-230 F to evaporate condensation in the crankcase. Your oil temperature is also less than coolant temperature, 186.8 F, which doesn't make sense if this is oil temperature exiting an oil/coolant heat exchanger. Why would Toyota measure coolant or oil temperature at the exit of a radiator or heat exchanger? When a technician wants to perform diagnostics, isn't it better to measure coolant and oil temperature exiting the engine block?

Have you observed an engine oil temperature reading in the 220 to 230 F range?

Allow me to clarify. If you're driving 25MPH or higher speeds, then yes 4H makes sense. In that case if you leave it to the car, you'll be in 4th gear...causing higher transmission temps. In that case keep it in 3.

No problem. There are many OBDII devices out there that will give you lots of vehicle information so I definitely recommend looking at a bunch and deciding what's best for you. I chose the Scangauge II because it's been around forever, reliable, and great customer service. It's a dinosaur but so is the 4runner lol. I like that.

I bought OBDLink MX+. It took awhile to set up 4 dashboards that gives me continuous real time data on my iPhone 8+ to the following parameters: 2 transmission fluid temps, coolant temp, battery voltage, 4 catalyst temps, 2 oxygen sensor voltages, 2 long term fuel trims, 2 short term fuel trims, total number of DTCs, number of emission related DTCs, total number of all cylinders misfire count, number of trouble codes, evaporator fin thermistor temp, and 4 tire pressures.

I have scanned for DTCs and none were found. I haven't tried the data log, monitor or mapping features. I will load OBDLink software on my laptop when the weather is cooler.

When launching the app, one has to select a connection to a particular system, such as Network A (engine, steering, airbag, a/c, driveline, etc), Tire Pres Monitor, Network F (vehicle body), Telematics, Immobiliser, and Occupant Detection. I haven't tried using the last 4 features. Note, each network is separate, therefore, when looking at tire pressures, one cannot simultaneously view engine data because each network has a different control unit.

Overall, I like how the information is displayed and I wanted something easy to use. BlueDriver is another one to consider. Google search BlueDriver vs OBDLink MX+.