Frigidaire Dryer heats once, then never again until restart

[SKB]

Frigidaire gas dryer FDG336RES1 will fire up, heat comes on for approximately 5 minutes, Vent temperature climbs to 138 degrees. Then the heat  shuts off and temp goes slowly back to room temp. Drum continues to turn. Is this a thermostat problem or coil problem or something else? I did turn it off once at 110 degrees, then shut the door and it continued to heat with increasing temps. Once it hit 138 I could not get heat to come back on without waiting for it to cool back to room temp. Thanks in advance

[SKB]

Also first thing I did was to clean out all the ductwork

[applianceman97]

Usually when a gas dryer fires and heats at the very beginning of the cycle but then stops heating has faulty gas coils. Sounds to me like this what you are experiencing.