I get the Tire Pressure Monitors Not Detected when I reach around 50mph. The sensors have been reset numerous times. Sensors have been renewed. The warning only comes on at speeds of about 50mph. The warning resets after stopping the engine. Anybody had this? Anybody know the cure. 

Sound like the new sensors are not calibrated. You can get it done at a garage or you can buy a ford trigger tmps tool.

With the tool here is the steps to follow.

 

"1. Make sure all tires are inflated to the vehicle specifications.
2. Make sure ignition button is OFF then press and release the brake pedal.
3. Hold the ignition button down for 2 seconds, release it, and then tap the button once. The vehicle should be OFF. Hold the ignition button down for another two seconds, release it, and then tap the button once.
4. Hold the ignition button down for two seconds again. The vehicle should be in RUN mode, engine off.
5. Press and release the brake pedal.

6. Tap the ignition button once so the vehicle is OFF.
7. Hold the ignition button down for 2 seconds, release it, and then tap the button once. The vehicle should be OFF. Hold the ignition button down for another two seconds, release it, and then tap the button once.
8. Hold the ignition button down for two seconds again. The vehicle should be in RUN mode, engine off.
9. The horn should sound letting you know the vehicle has entered into TPMS relearn mode.
10. Place the top of the FORDTRIGGER on the sidewall of the driver's side front tire in the location of the valve stem.
11. Press the button of the FORDTRIGGER tool. The vehicle's horn will sound letting you know the sensor has been learned.
12. Once the horn sounds, move on to the passenger side front tire and repeat the process. Each tire should only take 30 seconds or less.
13. After the passenger side front tire has been learned, continue on to the passenger side rear tire and finishing with the driver's side rear tire.
14. You may now turn the ignition to OFF. If the horn does not sound, the sensors were learned successfully. If the horn sound twice, then the process must be repeated because there was a malfunction."

Thanks for that, but to be fair, the sensors have been calibrated so many times it’s unreal. All is fine, until I reach 50mph, then the warning shows up.