That D looks like a midget next to that BIG boat...lol

 

when youa re towing heavy loads leave OD off even on the highway, just slow down a little and take it easy its better fo ryou and the truck

i turn it off for a few reasons, (ill explain how o/d off works after)

1) better engagement/shifts (firmer and less slipping into gear)
2) holds gears longer
3) as stated above you get a little engine braking effect out of it
4) better efficiency around town


the way the O/D off works in these trucks is very similar to tow/haul (some actually say tow/haul instead of O/D off). It locks out the OD gear, it firms up the shifts causing less slip of the clutches, it increases fuel efficiency by having a tendancy towards locking up the torque converter (much more than w/ O/D on), all of this does alot of good to help with the life of the transmission and the fatness of your wallet over time.

 

I always assumed it was worse for mpgs around town since the RPMs are increased.

 

Less of a load on the engine though. Plus the torque converter is locked up more often increasing transmission efficiency.

 

Read your owners manual, it explains what you need to do.

 

in practice your transmisison will shift into O/D below 45, in theorey this shouldnt happen, locking it out stops it from happening, and gives you better response when you step on the go pedal, if has dropped into O/D at 35, it will need to shift twice to get to passing gear if you need to really get moving, w/ O/D off it will need to make one shift. Also as stated witht he torque converter locked up there is a large decrease in losses through the transmission.