I always tow with OD off. Sometimes I use OD for a bit when going downhill.. I tow a 4000 lb travel trailer all over the place, Mountains, deserts, you name it. The truck will run all day long at 2300 rpms, thats fast enough (around 63mph} and I get between 11 and 13 mpgs depending on wind and terrain. 50,000m miles most of it towing.

 

This is been an interesting post...

I pretty much always turn over-drive off when towing heavy loads. The truck tows better and it drives me crazy when it keeps shifting back and forth to hold highway speeds.

I think an interesting point is that, on a GM truck, the over-drive button is actually labeled "tow/haul." That seems to say the manufacturer recommends turning over-drive OFF for towing.

Also, I have an old 4Runner (1991). I used to drive to the beach in college with a car full of people and luggage. If I did the drive with over-drive on, the tranny would over head, the light would come on, and I'd have to pull over to let it cool while the engine was at idle. If I did the drive with over-drive off, I never had a problem.

 

I have a 2004 f150 with the 5.4 and 3:73 diff and tow a travel trailer that is 6800lbs loaded. I drive between 60-65mph with the OD off for about 1000-1500miles each trip. I do this 3-4 time per year and have been doing this for 5 years. I came home after one of the trips and changed the tranny fluid and brought it in to a tranny shop. I was told the tranny fluid was clean. This was after a trip I went up a 7% grade for 15miles plus numerous other hills in BC, Canada. The truck stayed in 3rd at around 50mph at 2500rpms on the big hill. Cooling fan did not even go into high speed. Outside temperature was 90 degrees. Truck is stock except an extra leaf in the springs. I can put this trailer on without my WD bars and the truck sinks 1". Of course I always drive with the bars on. I sometimes drive with the OD on with a tail wind or going down any small hills. Otherwise OD on going up hills and down hills. I end up driving slower going down hills the up. Have no transmission temp gauge, so no info there. There is my 2 cents anyway.

 

I tow with OD on unless it's hunting...

 

UPDATE on tranny troubles,

Last week over spring break the 4X4 transfer case went out less then 50 miles from home, needless to say I had to drive the entire week in 4WD on dry pavement despite what the owners manual says it was the only way I could go forward without the truck sounding like a bag of marbles inside a coffee can.
Truck is back in the shop for the 6th time waiting on a transfer case, looking to trade for an F-250 very soon.

 

interesting-with my 93 octane troyer tow tune- i have zerio issues with gear hunting-much different shift charac teristics than his perf tune