The truck is an 05' GMC Sierra, ext cab., 5.3/4L60E setup. No trans temp gauge but a factory trans cooler (tow package). No engine or trans mods, all stock.
I was cruising from Los Angeles to Lake Havasu, AZ last weekend with about 300lbs in the bed and another 500lbs (JetSki) hanging off the rear bumper. I've made the trip a dozen times in the past without an issue. I had Tow/Haul mode on since I left the house and was on cruise control at 75mph. About 30 miles outside Havi I started up a slight grade but nothing crazy and only about half a mile long.
I noticed all of a sudden the RPM's creeped up to about 2500rpms and it sounded like the trans was struggling. Right at that point I got the infamous "Transmission Hot" on the dash. I took off OD and limped her the rest of the way into town.
I got to my buddies shop and put her up on the lift. We noticed some fluid had come out of the overflow tube. We checked the temp with an OBD II reader and it was at 177*. Trans fluid was overfilled according to the dipstick.
Now, the original trans was replaced around 33,000 miles from the dealer (under warranty) because it was making some noise. The truck now has 162,000 and nothing has ever been done to her. Never a flush, filter change, nothing. For 130,000 miles, the fluid actually looked pretty good and it was never changed because we waited to long and didn't want to lose our clutch material in the fluid.
So, curious if it's worth at least dropping the pan and changing the filter and some fluid or just plan for a new trans sometime in the near future. All the rest of the gears seem to be holding, only overdrive had that issue and only when there was a "load" on the truck. Hasn't done it since and I've daily driven it the past week to work with an empty bed. Thoughts?

 

Maybe the torque converter lockup is slipping? Isn't it a bad idea to tow in OD? At those miles you could have worn clutches too.

I'm no pro. Wait till the smart ones chime in.

 

The converter lock up clutch is probably about done, the tcc slipping will bring the heat up quick.... Towing in od on long flat staright aways should be fine, but on inclines you wanna drop it down to drive even in tow/haul.... Esoecially wuth cruise set... Shoukd be fine to change the filter and fluid, if there is material in pan or the fluid is black, plan on a rebuild soon.... Suggest at very least a new converter, especially if you plan on making that tripnon regular basis!!

 

Thanks for the insight. Fluid actually looked pretty good for 130,XXX on it. If I drop the trans for just a converter, I would probably just swap in another trans along with it at that point. And if that's the case, any advantage to changing the fluid and filter before then or just keep her together and run her until she's done?

 

Wouldnt hurt to change the fluid, but if theres a bunch of material or whatever in pan, be prepared to start at least looking at rebuilding it or buying anither unit, if pans fairly clean, just run it.... There will be some material in the pan that is normal, but if there is a bunch its not!!! Iirc gm recommends, 75-100k before fluid change anyway!!!