Towing Issues: OVERDRIVE, gm trucks, diesel trucks

Question
When towing my RV I always activate the "overdrive off" button on my truck. A friend and I were talking recently and he told me to "engage" the overdrive when climbing a hill. I thought this would stess the transmission due to the constant "downshifting". I need an expert to tell me when to and not to use the overdrive function on the truck.

Answer
Paul,

I hope by "engage" your friend meant push the button so the light on the dash is illuminated.  Althouh this does in fact disengage/lockout the overdrive function it can lead to some confusion.  

Overdrive should be locked out when towing a heavy load.  In fact you may want to force the transmission to a lower gear to climb a steep incline to keep the transmission from shifting back and forth between gears.  

On some trucks this button is labeled "O/D" while on others, including most GM trucks, it s labeled "Tow/Haul".  The newer GM H/D Diesel trucks now have two functions to the button.  A brief tap of the button will lockout overdrive while holding the button for a couple seconds with enter a Tow/Haul mode with more efficient engine braking and longer runs between shift for better use of power.

Good luck,
Shayne Peterson
MobileHitch
http://www.mobilehitch.ca/