I have a 1999 ford 150 automatic, when driving at 45 to 65mph it wants to down shift instead of pick up peed or kick into overdrive. The only time overdrive works is when taking off and pushing O.D.b

Depends if you have a regular 3 speed automatic, or a 3 speed with overdrive.
Put it in drive, it will start out in first gear, then shift into second at about 15 MPH, into third at about 30-35 MPH. With overdrive, fourth gear will kick in at about 45-55MPH.

check your linkages from your gear stick to the gearbox .need adjustment.and check the kick down cable ,at the throttle needing adjustment.

change electronic module on side of transmission

It will shift out of overdrive upon increasing throttle , pulling hills and so on. Your overdrive probably kicks in around 35 to 45mph and kicks back out as you increase throttle. Electrically controled speed sensor to control the response. Overwise the engine would bog down to a stall. Over drive is just that. It changes the gearing ratio to over drive meaning less then final gear 4 to 1 down to 4 to 3 etc more direct drive ratio to lessen consumtion of fuel with less stress on engine. Have shift speed sensor adjusted. Don't drive in overdrive in city if most driving is under 45mph

Problem probably solved right here!

Sounds like the passing gear cable is out of adjustment. Get a shop manual and see what the specs are on how to adjust it properly. It is a pretty simple fix.

juan: there is a cable which comes from the transmission to the throttle linkage. This is called the TV (throttle valve) cable. This is designed to work in conjunction with the position of the throttle. I'm sure you heard the term "KICK DOWN SWITCH". Well this essentially is doing the same thing. If the cable is out of adjustment, it will have a tendency to want to downshift into 3rd.
Even though overdrive is electrically actuated, it can be disengaged by the throttle position.
There is also a coolant temp sensor which keeps the transmission from shifting into overdrive until the coolant temperature reaches a certain point. The sensor tells the ECM to tell the Solenoid it's ok to supply a ground to it.
Your overdrive switch provides a ground to actuate the overdrive solenoid. Make sure the switch has a solid ground serving the circuit.
The torque converter solenoid picks up it's ground from the ECM.
Both solenoids are served by the same power source which is a switched circuit through the ignition.
I hope I have shed some new light on your problem and given you some new direction in which to look. I hope I have helped you resolve your problem. If not, I'll be watching and will be ready to offer more help if needed. ..mybunkey

When the car is just cruising along at approx.50+ MPH push the O/D button. You should feel the gears change higher and if you have an RPM guage then it should drop as well to fewer RPMs. This would be normal driving conditions. O/D will not kick in until the last regular gear (3rd or 4th depending on model)  had been shifted into. O/D automatically kicks out when slowing down and the transmission shifts to a lower gear. Thus the O/D has no function at slower speeds/gears and does not need to be shifted ( on or off ) except in the very first example given here.

Test the transmission module. It controls everything the transmission does, the timing of shift points, gear selection, overdrive, etc

How many miles on it? Do you mean overdrive? Over drive will clunk when shifting in cruise. Mine lasted 212,000 miles but I have heard of them going out after 120,000, depends how you drive. That Traney is good till it starts acting up then you will need a complete overhaul. I got it done for $1800. Do not go to a Ford dealer, they quoted me $3200.
Jeepgreg