Hi,Welcome to Just Answer, My name isXXXXX will be helping you with your appliance issue today.
Good afternoon, this is a single heating element in it and normally these either go completely or heat, you may have a bad thermostat however, can you do a little test? You've already cleaned the vent going outside can you tell if the air flow is real strong outside? Try removing the vent from the back of the dryer and starting it check the air flow coming out of the back of the dryer and let it run for a little while and see how hot it gets coming out the back, how long a run is your vent hose going outside? in feet?
the run is about 12' --- the airflow is real good but the temp is closer to warm instead of hot. i tried that when i cleaned it out.