Originally Posted by Rockypointers
snip....... I have a 2010 F150 5.4L V.8.....so the "overdrive" is actually a "Tow/Haul" button on the side of the gear shift lever.........snip
Check your F150's owners manual to confirm the actual function of "your" Tow/Haul feature. In the case of the Tow/Haul feature on my GM TV, when engaged it will add about 500 rpm to the top of each gear before shifting to the next gear. I do know that there are some Tow/Haul systems tied in to the overdrive gear, but check your manual.
If you find that your transmission is "searching" for gears often, then it's best not to tow in overdrive.
If your F150 5.4L drivetrain's Tow/Haul is strictly for adding RPM to the gear shifting range , IMO always tow with it engaged.
Also, most gas engines will produce some RPM's (within the torque curve) when towing through the mountains, especially when towing a heavy load.