Regarding a 20-year-old Kenmore I had a dryer vent service come out a few months ago; they cleaned and made sure the vent was securely attached in the attic where it vents out the roof. That seemed to fix the trouble for a few months, but I'm back to not drying unless I re-rerun at least twice. It's very hot. The drum is tumbling. My vent hose is clean (but I have no ability to get to my attic by myself to check through the wall.