I have a heavy duty dryer through which I have to put a load twice before it's fully dry. Lint Filter clean. There is some heat just not enough to do a large load!
Any suggestions?

Check the venting duct for obstructions. Check the "flapper" on the outside of the house, is it "flapping" freely?

This can be a fire hazard - although if the dryer isn't getting extremely hot, it sounds as if the high limit thermostat is functioning as it should.

Could be the high limit thermostat is kicking out at too low a temperature, or the low limit thermostat is kicking in too high.

Check the vent first, though.

Stew

Thanks Stew. Will try that first and see what happens
ML