I have had mine up to 220 F after miles of hard/fast driving in sand. This caused fluid to leak from one of the cooler fitting/rubber hose connections.

 

I am using a new autometer ultralite temp gauge and the sender is a single wire electrical one. I was in 2wd the whole time I was off-roading...nothing too intense. I'll have to see if I can pickup a temp gun for a reasonable price and check it. I did touch the tranny cooler while I was out and it was quite hot.

 

Temp gun can be had for $20 delivered and they are very handy.
When you get one, test the temp of rear differential after wheeling, just to see how hot it is getting. Normal temp for running on highway is 135 F +-.

 

I got my infrared temp gun in and checked the rear end and it was 140F. The transmission pan is about the same temperature that my gauge is reading also. I moved the cooler in front of the ac condenser on the passenger side where the clutch fan is.

I hooked up my trailer with a lite load (~700Lbs total weight) and took it uphill. The temp barely went above 180. I had it shifted in 3rd gear the whole time going uphill at about 55mph. Took my car back home and unhooked the trailer and went uphill in another area and did small off-roading and it cruised back up to about 220. I have noticed that any driving that is requiring the car to shift more is causing it to heat up. I did some driving uphill where it was shifting between 2nd and 3rd gear and it heated up to 220. Also doing in town driving is getting it up to 190+ Is it possible that my clutch packs are wearing out? My car has 178K miles on it and is probably still on the original transmission.