My scenario was different then whats been happening on the boards. I knew I had a bad sensor when my left rear looked like a pin cushion from all the roofing nails that spilled on the roadway. When I hit the nails, I got lucky and only one tire was hit. I couldn't pull off safely fast enough , so I knew I would probably have problems with the sensor. When getting new shoes I found out my sensor and band snapped. I attempted to use a new strap with the old sensor and was keeping the fingers crossed so wouldn't need to replace it. Surely enough that lasted about a week. So I ordered a new sensor.

About your problem. I had issues with the TPMS when I was just using air and I've had far fewer if any when I switched from air to nitrogen filled tires. When I had air the tires seem to fluctuate the pressure thus tripping the sensors. Since I've had the nitrogen I rarely need to get them filled and no problems with the tpms.

Also did your mechanic use a device to check the sensors? You don't need to take off the tires to do this. The device will read if the sensors are working properly or not.

Sorry I can't be more of help. But you do have some great people here that can help. You may want to record a little history of when and what the truck is doing when your sensors trip. The more info you post, the better it will be for someone to help you out.