Mine is tapped into the hot side. It sits dead for a couple of min then comes up to 165 in traffic. Drops to 150-155 while cruising down the interstate. You may have seen my previous post about my aux transmission cooler line coming loose. This is when I really started to watch the needle move. As a matter of fact my eyes are now FIXED on that gauge

 

Mine seems to hold around 160* during *normal* driving. But I've noticed it more-or-less mirrors what the engine coolant gauge is saying. That's why I've had a hard time, with mine at least, trying to determine if the coolant is effecting the transmission fluid, or if the transmission fluid is effecting the coolant...since they both rise on long grades. Temp sender is in the pan on mine. It's a double deep Mag-Hytek. Tranny temp also definately goes up in town driving or with lot's of idling in gear.

I would expect your tranny fluid to run cooler just because you have a DTT 89% tq. I have the sloppy chrysler snow-mobile version...runs the same rpm at any speed!

 

Mine runs about 170 at highway speeds, the temp will vary depending on if its before or after the heat exchanger. Our trannys like 180 degrees best, its their normal operating temp,

 

If you are still using the little cooler that came with the truck, I would get a new larger unit installed. I did when I had trans rebuilt. I never see a temp higher than 160 when pulling a fully loaded 28 ft fifth wheel. It takes an hour or so of driving to see 120 with just the truck.

 

i've never seen mine go much past 140. im not sure where the sensor is, as i havnt had the change to search for it yet. what is the ideal placement for the temp sensor?