Kenmore gas dryer intermittently working

My Kenmore 110.70936990 model dryer was sometimes not starting up after I'd press the start button.  Later it would.

9 months ago, a repairman replaced the motor relay switch and that didn't resolve the problem (it’s slowly gotten worse).

8 months ago, I changed the start switch and that also didn't resolve the problem.

It got to the point that I'd press the start button several times and finally it would kick in and work fine.  However, recently, that hasn't even worked consistently and even when it did finally start, it would sometimes just stop again 5-10 minutes later.

Recently, I bypassed the thermistor and plugged the leads from the old thermal fuse to a brand new one. Still no change.  The drum turns as long as I'm holding down the button (so the belt is OK).

I've opened the door and pressed down the piece that activates the door switch, held down the start switch and the drum turned, so the door switch seems fine too.

After not working at all for almost a week straight, it did fire up again one time, but the dryer ran for about 5-10 minutes total, started off normal, then gradually started sounding rough and somewhat shaking, got louder, then stopped making the noise…and then ultimately stopped running again. The sound was like something running over rollers, a grinding type sound.

I called the same repairman as before and he said the only thing it could be is the motor…so he replaced it, vacuumed out the mechanical areas of the machine. It ran fine that afternoon…until he left, of course.

It’s still doing the same thing it was to begin with. Press the start button, starts to spin, stops after releasing it. I asked him to come back. It again started up fine in his presence…grrr. However, it did stop mid-cycle and he saw that, but couldn’t find a reason why it did that (I’m starting to question his abilities, honestly.)

He left after not finding anything crazy except a “fiber in front of a sensor” that could be throwing something off. Then again…next day, same issues. So, I removed a few wet clothes (not a huge load) I wanted to attempt to dry…and pressed the button again, it started. Weird. Put the clothes back in and it started up but didn’t dry completely after 40 min. Was able to get it to start again and it ran another 40 min. and still was just “mostly” dry. (Update…I just realized why THAT is happening. I watched it as it stopped spinning/drying mid-cycle and then noticed that the knob turned fairly rapidly to the end and clicked off. That’s why it looked as though it ran thru the full dry cycle but the clothes were still damp.)

What is wrong with my machine?! HELP! I feel like the repair guy is just guessing and swapping parts and not getting the root of the problem.