Finally got my scangauge upgraded, which by the way is free if you walk it into their office here in phoenix, and can finally get transmission temperatures. I thought I'd post what I've observed so far.

Stock 2007 4runner, V6, with Duratrac 265/70-17 (1 inch larger dia).

Today was the second day of use and during my commute into work with temperatures around 90, the transmission stays around 170 deg on the freeway. If I hit stop and go traffic it'll go as high as 190 and if I stop for more than 10 seconds it'll go to 195-200.

When I started the engine at the end of the day, the tranny temp was still 124. For my commute back home, ambient was about 115 with the dash thermometer saying 117. The hottest it got from an on ramp run was 216 deg and it didn't want to get below 200 for the rest of the commute.

I'd be really interested to see how hot it gets while towing my popup trailer to the mountains.