6L90E Transmission temp

[MJN]

Looking for some advice or maybe reassurance here- 2012 GMC Sierra 2500HD 6.0L, 6L90E trans, 3.73 gears, 129,000 miles.
No issues that I've noticed, truck drives and shifts fine, no codes or anything. I started to notice the transmission temp seemed to climb faster than normal and not cool off nearly as fast as I had previously seen. Today it was in the mid-80's and humid, cruising on the highway, empty truck and not towing, the trans temp stayed around 145/150. I towed our camper to the state fair grounds and I kept it in Tow/Haul mode, shifted into M and selected 5 so it wouldn't shift into 6th (not that it would anyway). Everything seemed fine, truck seemed gutless as usual pulling a 8000 lb camper and wouldn't hold 65mph and was shifting between 5th and 4th. 4th gear at 60 to 65mph is around 3000rpm. The trans temp climbed slowly as expected and reached 180 eventually, it did cool down a bit closer to town and traffic slowed. After dropping the trailer and heading home on the interstate running 75mph the trans stayed around 155/160 with just an empty truck. Closer to home, on the 2-lane highway running 55/60mph it still stayed around 145/150 but just going up a hill with light throttle it would jump to 160 and take a while to cool back down. I don't ever recall it warming up so fast and taking so long to cool down before. Nothing blocking the cooler up front either. I just changed the fluid and filter 1000miles ago, the pan had some gray sediment in it but nothing sparkly or concerning. I checked the fluid when I got home, right at the full hot mark and bright red, idling in the driveway at 162 degrees. I'm starting to worry the torque converter may be on its way out, otherwise I have no idea why it would heat up so fast. No slipping or lazy shifts, it shifts firm and fast, just concerned about the temperature. Any thoughts or things to check?

[Accelo]

175F to 200F is considered the ideal operating temperature for a transmission (Other sources say 160-180), and 150F is considered the minimum ideal operating temp.

No worries, may just be different weather.

[MJN]

Alright, thanks. I'll keep an eye on it. I did order a new baffle that goes on the radiator support to help direct more air into the cooler, the original one is damaged and missing the side flaps so might be losing air flow off to the sides instead of going through the cooler.

[JJH Jimmy]

The converter was probably not locking up while you were towing the camper in return slipping and building heat. 180 isn't anything to be concerned about.

[MJN]

Originally Posted by JJH Jimmy

The converter was probably not locking up while you were towing the camper in return slipping and building heat. 180 isn't anything to be concerned about.

My understanding was that in tow/haul the converter locks up in 3rd and I was running 60 -65mph so it was in 5th on the flat stretches and downhill and 4th if we were going up hill. But the shifting between 4th and 5th would create heat for sure.

[95 S_Trucker]

I regularly tow 8,000-10,000 pounds with my 2011 GMC 2500HD 6.0. Mine has 4.10, so its rated to tow 13,500. Anything under 215 degrees is fine. 180-185 is ideal. 150 or lower is too cool. Dexron IV fluid doesn't brake down until 250+.