Cold North Country

Good infos. I did same, BET, but have both original upper factory check plug and added bottom drain plug. Also did the stick tube for refill. Here a pic of mine at 33k milles at first service.

OP signature say 2020 GMC HD so assume 6 speed. I also have 2020 with 6 speed. Yes GM state all different fluid for 6, 8, and 10 speed, all use different fluid. Thanks

Is the GM oem 153 Thermo readily available, and if so where?. Dealer said will not replace under bulletin unless there is a problem. Why does GM want the Tranny to run so hot? Is there a reason?

Thanks for the infos. Sounds like synthetic is the way to go with GM wanting the Tranny to run so hot from the factory thermostat. Still wonder if they factory fill with synthetic or mineral?

-I have been wondering the same thing for both the Tranny and the xfer case. What actually is put in at the factory? -Summit Racing stocks 2 different ACDelco Dex VI, one says Mineral in the specs but nothing on the container, and the other says Synthetic on the container. Mineral: ACDelco 10-9395 ACDelco DEXRON-VI Automatic Transmission Fluid | Summit Racing Synthetic: ACDelco 10-9244 ACDelco DEXRON-VI Automatic Transmission Fluid | Summit Racing