2007 F150 Screw 4x4

This past fall, I bought used OEM wheels to use for winter, along with winter tires. Before mounting the tires, I bought OEM Sensors and bands. When I got this "new" wheel package installed, I had to take it to the dealer to get them to reset the TPMS, as I was getting a "fault" message on the display. All was good all winter, then recently I went back to my factory wheels and tires for summer. Now my "TPMS Fault" message is showing again. I spent time on the forum here and learned how to enter "Relearn" mode (ignition on/off 3 times, brake pedal, etc), and I get the 2 horn honks and a message to relearn the LF wheel. I have a strong "welders" magnet I'm using, but to no avail. I can never get the 1st wheel to sync. Do I need to buy the tool from Ford? Stronger/different magnet??? What do you guys figure?