OK. I found some really good about the AT Temp for the 750F (sealed) transmission unit.

arty: :drum:
Source: 2008 4Runner Limited Field Service Manual (FSM)
1)
"Normal" operating range for the transmission is 122F to 176F, although the temp can and will go higher.
(For me this means that I will add a bypass lever or make a cover for my 2nd aux trans cooler for use while NOT towing during the cold winter, because my trans was running a little cooler in the winter when not towing.)
View attachment 247087
2) The A/T Overheat light comes on at 302 F !!!! ... and turns back off at 275 F
(Note the typo in the FSM... 150C is 302F, not 275F)
View attachment 247089
The A/T Overheat light comes on at 150 C (which is 302 F !!!), and goes off at
130 C (275 F) (The chart has a typo on the conversion from 150 C).
This means that you could heat your trans fluid all the way up to 300 F, and STILL not have the overheat light come on !!!!! It also means that when the overheat light goes off, you're at 275F, and can go all the way back up to 300 F without the light re-illuminating.
Clearly the light is only a warning for the truly extreme over-heating situations, and should not be relied upon to see if everything OK while towing. On a long trip, you could (theoretically) have your trans temp at 300 F for a good portion of the trip, and your A/T Temp light would NEVER turn on!
3)
Temp measured inside transmission where newly cooled fluid re-enters the tranny.
This temp is measured where the fluid returns from the transmission cooler and enters back into the transmission unit itself. Also, towing, hill climbing and traffic can rapidly heat up the transmission.
(Quote)
The No. 2 ATF temperature sensor is on the transmission, just in front of the oil cooler inlet pipeline. If the ECM detects an abnormally high ATF temperature near this sensor, it illuminates the warning light.
HINT:
--The temperature of ATF easily rises when towing, climbing hills, in traffic, etc.
(end quote)
View attachment 247091
4)
The trans temp easily rises while towing, climbing hills and in traffic.
5)
If you're trans gets too hot, let your engine idle in "P" or "N". Don't turn your truck off to cool down an over-heated trans.
View attachment 247090
Hint *2 tells us that the transmission should cool to less than 135 C (275 F) within 5 minutes the engine idling while in "P" or "N".
6)
Tow on the highway with the shift lever in "D" or in "4".
In "D", the trans will lock-up in 5th gear. Shift to "4" if you want it to lock up in 4th gear. Locking up in 3rd gear can make the trans very, very hot (>266 F)!.
Hint *1 tells us that with the shift lever in "D", the transmission will lock up in 5th gear (lock-up is good!), and that if we change the lever to "4" that the transmission will lock up in 4th gear. So it's OK to shift to "4" when towing if you need some extra torque and power.
The table also indicates that when the transmission locks-up in 3rd gear, that the trans temp can get very high (>266 F), so I would avoid extended periods of towing on the highway in 3rd gear.
7)
The Transmission has two different temp sensors...
The first is inside the transmission unit itself, and the second is at the front of the transmission where the newly-cooler fluid re-enters the transmission. Overheat conditions are based on the 2nd temp sensor, which seems to be the sensor that my Ultragauge Blue is reading.
Hope this helps! :rapture:
-Phil