[Crasen]

My words exactly, place transmission in drive never overdrive when towing or carrying heavy loads, I am sure if you read the owners maual (if you have one) it will tell you this. I would say your transmission is getting hot. You might try cleaning the outside of the tranny cooler. If the outside is dirty it can slow down the heat transfer from the tansmission fluid to the air passing through the cooler. If you have a fin type tranny cooler you could try upgrading to a plate type cooler, I would only try this if you know the fluid is getting too hot and the above doesn't seem to work.