It doesn't matter what year make or model if your towing you should turn off the overdrive or put the vehicle in tow/haul mode. When pulling a heavy load the transmission has to down shift a lot to be able to go up even the slightest grade. Even more when in overdrive. The purpose of overdrive is to lock the torque converter so that there is no slippage between the engines crank and the transmission input shaft. This is done to give you better fuel mileage. Every time the transmission locks and unlocks the torque converter it builds up more heat. While towing this heat is built up faster than the trans cooler can dissapate the heat. Thus cooking your internal trans parts. You will notice that your gas mileage will suffer and engine rpm's will be higher but your trans will go through less wear if you turn off your overdrive. If concerned about mileage leave the overdrive on and monitor your engine rpm. If you notice the truck shifting a lot(rpm going up and down), turn off the overdrive. Make sure you check trans fluid before you leave and after you get to your destination and before you shut off the truck let it idle about 5 mins before you shut off the engine to allow the internal trans parts to cool some from the circulating trans fluid. Remember that an overfilled trans is just as bad as an underfilled trans. If any thing here I wrote is confusing say so and I'll try to explain better.
