Towing in overdrive or pushing the O/D button in

The only time you need to turn off Overdrive is if the transmission is "hunting", meaning it is frequently shifting between drive and overdrive. The only other time is when you want to use the engine for braking.

I tow nearly 100% of the time in OD, and my combined weight is usually around 22,000 pounds and can top 25,000 on occasion. I have 358,000 miles on my transmission.