When towing with my 04 F-150 HD and begin climbing a hill, transmission downshifts from OD (as it should) but the RPMs aren't as high as if I lock out OD and tow in 3rd gear. What is happening here. I have the XL so I don't have tachometer so I working by sound here. Thanks for any information / Skip

 

I don't think you are suppose to tow with the OD on... I've always heard it is REAL bad for the tranny

Is this correct?

 

Owners manuel says as long as it's not shifting back and forth it's no problem. Always towed on OD on my 01 also but it didn't take much of a hill to get it out of OD.

 

I responded to your OD question in one of your other posts. As for towing in OD, turn off OD if it hunts between gears regularly to reduce heat.

 

What you are experiencing is your torque converter unlocking. A lockup torque converter kind of gives you a semi-extra gear.

When accelerating to hwy speed for example. Your transmission shifts into OD and shortly after the rpms drop about another 100-150. That is the torque convertor going into lock-up mode. When accelerating slightly, or going up a hill, it will unlock before downshifting to 3rd.

Note* Only tow in OD with a very light load. Excessive downshifting as well as lock/unlock of the torque converter creates extra wear and excess heat. The decrease in fuel mileage from driving in 3rd is cheaper than a future transmission failure.