over drive

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I would read the owner's manual. I use overdrive in my F250 SD towing a 5th wheel. When it downshifts, I turn off the overdrive to prevent it from hunting gears (shifting up and down often.)
Yes, it's just another gear in the tranny.  If the truck will stay in OD and not continually shift back and forth, go ahead and use it. Of course it will shift itself on little grades or when you accelerate, but that's normal.  But if it is shifting in/out all the time, lock out the OD and let it stay in the next lower gear.
Thanks guys didn't even know it was something I might have to think about until I started reading past posts. This forum I great
Something to be aware of is some transmissions have two modes of operation - with the torque converter locked and with it unlocked.

When the torque converter is unlocked, it's slipping through the hydraulic fluid and adding to the heat buildup in the transmission.

I have a Toyota Tacoma work truck that will shift from locked to unlocked while still in overdrive.  If I manually downshift out of OD I can maintain the same road speed with less throttle pressure, at the cost of maybe 100 extra RPM.

If you have a tachometer it's easy to tell which mode the torque converter is in.  Just press a little harder on the gas pedal and watch the RPMs.  If the converter is locked they'll stay the same, increasing only with road speed.  If they rise without the road speed changing, the converter is unlocked.

You need to check your owners manual as well as the dealer. Most over drive (gears) are not designed to with stand the pulling weight other then the vehicle itself. I learned the hard way just by pulling a utility trailer from Ohio to Missouri several times. Then I read the owners manual and sure enough it said do not use overdrive to pull a load. That was over $950.00 fix back in 1985....
Back in '85 that was probably the torque converter lock-up that Lou mentioned. Modern trannys will have both the lock-up (much improved) and an actual OD gear. Or maybe two. My GMC Acadia 6 speed auto has 4 "main" gears and two OD gears, and so does the Allison 6-speed in my coach. Nothing very special about them except that the gear ratio is less than 1:1, meaning it multiplies rather than reducing.
I use my MH 90 percent of the time towing my race car and golf cart to the track. It stays in over drive most of the time. It only shifts out on some steeper grades. I've also used my 05 chevy pick up to tow it with and have no problems. I used tow haul mode on the truck before, but it only uses more fuel, can't tell much difference other wise. I did notice when I was shopping for a coach that some shifted out of over drive quicker than others on about the same grade.
Generally there are two considerations when considering overdrive.

MOST owner's manuals say "Do not use when towing".. I do understand why.

However the other consideration may be of more interest.

IF with over drive on, it kicks in and remains engaged... Use it.

if it keeps cutting in and out, "Hunting" as it were for the best gear ratio.. Turn it OFF.
Makes sense to me I appreciate all the input. Think I'll just take it out of overdrive and lose mileage rather than experiment and possible do some damage that may cost ( probably much more) than a little extra fuel per mile.

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