Seeing a movement of nearly 90 degrees F in just 4 miles seems high to me, unless it was over a stop-and-go period where time was a factor also. Had it levelled out or was it still climbing? By comparison, I recently drove my 4Runner 6 miles to a car wash (couple of brief stoplights, mostly 40-60 mph speed), washed it and returned home (12 miles round trip) while monitoring trans temps through the journey. I saw temps rise from about 70F (ambient) to a pretty level 135F. Granted I didn't have to sit in traffic, nor was I climbing hills or driving anywhere near "spirited." With that said my 4Runner weighs at least 1,500 lbs more than the Lexus and rides on 33" tires, theoretically working the transmission harder than the Lexus in a like-for-like drive. How big is your cooler? My cooler on my GS is a B&M 11" X 11" X 1.5". The 4Runner is only 10" X 4". Also curious - do you know the history of your transmission fluid? Is it fresh?

For my Lexus, I use a generic bluetooth code reader, which tied with the J-spec protocol in my Torque App, can read a number of parameters from the Aristo ECU - such as coolant temp, throttle position, RPM, etc. But not trans temp, unfortunately. I need to provide the specific PID for it to read from the trans temp sensor - which I do not know. I'm not familiar with the scan tool you are using, but wondering if it provides details about the PID/address from where it is pulling the trans temp, along with any of the calculations to turn the reading into a temperature?