Let me remind that under about 45 mph OD will not be upshifted too under any circumstances button on or off.
City/town driving under that speed with OD on makes no difference.
As an example gear ratio with 3.55 out of OD is 3.55.
With OD engaged over 45 mph the overall gear ratio is 3.55 x .7 = an overall ratio of 2.485 and a loss of torque mutiplication along with it.
Since most cruise at about 60 mph the engine RPM is about 1500 rpm +/-.
At this RPM the engine torque is low.
As the engine RPM gets up to about 2000 RPM, the engine begins to make a notable amount of extra torque and really gets with the show at about 3300 rpm.
The problem comes from the normal running RPM of 1500 to 1800 where torque is low causing poor throttle response in OD above 45 mph.
With 95% of noraml driving, the PCM takes care of all the shifting as it was designed to do. Trying to help with manuel control does not result in much help.
Even use of cruise contol on roads where the system down shifts on hills a lot is not much help for fuel mileage.
What you save on the level in cruise is lost on down shift time at higher RPM on a grade with the cruise trying to maintain the set speed. The RPM has to go up until the engine can pull the total weight at the set speed on any given grade.

 

At 40 switching the OD off shifts gears on mine. increase of couple hundred rpm

 

There can be small difference in what speeds are observed in different trucks.
The speedo is often not accurate.
The usual upshift speed is close to 45.
There may be some hysterisis on down shift because the program uses different program lines for upshift and down shifts..
The difference is your forcing the program with the switch and not with driveing and load control changes.
My speedo is about 2 mph fast so the accuracy is not that specific.
A word in the program ID block holds the gear ratio and tire size bit info so who know what's in there. It affects the speedo display as well.
This word data is the location programmers try alter to get the speedo to match tire sizes and gear ratio changes.
Bottom line is under a certain min engine operating conditions the OD will not upshift no matter what the switch is set at.
Everytime the PCM is shut down the OD switch function is automaticaly reset to ON, in program.

 

Sort of a thread hijack, but related.

Will the TC lock in third gear? In my Isuzu Trooper, the TC would lock in both third and fourth gear. I have no idea about my F-150. Sounds like no.

 

Yes, it can lock in 3rd.

 

Yes, the converter will lock up with the O/D turned off.

I don't touch mine unless I'm towing heavy.
With small trailers like my 4X8 utility, or the HS Band's ATV on a 5X10 trailer, I leave it on.
The Band's equipment trailer (16ft car carrier) and my boat (26ft Leisure Cat) which is about 6100 lbs, it's off.

I have also upgraded my trans cooler to a Superduty cooler from a 7.3 diesel.

 

I would just leave the button alone unless you know you are towing heavy or hilly, or if the transmission seems to be hunting gears. The more the TC stays locked up, the better off you are for heat purposes.

 

I turn mine off when going up or down grades, towing or not.. Even a 5% grade at hwy speeds often causes my truck to downshift running empty.. Going down, it keeps me from having to ride the brakes as much.

230,000 miles on my trans and engine and it's not died yet!

Mitch