The burner is on for 25 seconds and shuts off for 70 seconds.

I connected a test lamp to the high limit switch, as soon as soon as the test lamp goes out the flame goes out. About 30 seconds after the test lamp lights again the flame returns. this cycle repeats for at least 2 hr.

I jump the high limit switch and the flame stays on for an hour and then the other thermostat opens and shuts off the dryer.

I have tried 2 new high limit switches and both switches do the same thing. The original switch had 180-40F temperature rating. I tried a 200-40F switch and a 180-20F switch. The air flow from the dryer with high limit switch connected seems cool with a strong flow. I have replace both coils.
The dryer seems to get quite hot with the high limit jumped after about 30 minutes . I do watch the dryer continuously when the high limt is jumped.

I did not get an exact replacement high limit switch because the model number is not listed in most listings.