Lately my Maytag LDG9306AAE gas dryer started taking a long time to dry clothes. Like 2 hrs. or more. I checked the vents and it was pretty filthy even though we clean the trap after every load. So I vacuumed out everything I can get out without taking the vent assy. apart. It seems to have good air flow. I watched the burner with the front off and it starts and only runs about 30-45 seconds then shuts down. I tested the high limit thermostat and thought it was defective because I can bypass it and the burner will run for at least 2 minutes (that's as long as I let it run, might have gone longer) So I ordered a new high limit switch and installed it and the problem is the same. It will only run as long as the high limit switch is bypassed. I also noticed the timer advances normally in the regular and air fluff cycle but it won't advance on the auto dry cycle. Anybody got any ideas?

Thanks, Scott