Three primary factors are required for a dryer to function properly: heat, tumbling, and airflow.

How long the machine runs for a given load is determined either by the operator setting a specific time (Timed Drying), or by the machine's moisture sensor reacting to the dampness of the items (Sensor or Auto Dry).

Heat is generated by either an electric coil element or a gas burner, and controlled by a temperature sensor (thermistor).

Tumbling involves the drum rotating by way of a belt driven by the motor.

Airflow is by a fan pulling room air through the heat source, drum, filter, and blowing out the exhaust duct. Impaired airflow is by far the most common cause of poor performance. Insufficient airflow may cause the heating source to overheat and cycle on/off repeatedly on a high-limit protector, perhaps not reaching the target operating air temperature in the drum ... and of course also impair the machine's ability to exhaust moisture out of the load.

Erratic operation of the temp sensor and moisture sensor can also be a cause.

Agree with dadoes.....with particular emphasis on "Impaired airflow is by far the most common cause of poor performance."

From what you wrote, I wouldn't do ANYTHING else until I verified the vent-path is clear and free-flowing. May be messy, but otherwise pretty straightforward.

Thank you both. We do regularly clean the lint filter in the dryer and where it exits the basement to the outside. Time to get one of those long brush things and clean the whole thing.

".....clean the whole thing."

YES!!!!!

Please come back and tell us what found.

Is the room it is in humid? I have the back rooms of my house closed off to keep the rest of the house cool. One of those back rooms is my laundry room. When the room is humid my dryer does a real crappy job of drying.