Sorry to bust your bubble but you completely missed on the caller today with the clothes dryer taking three cycles to dry.
This is THE CLASSIC sign of a clogged or restricted flow dryer vent. It is not unusual for a dryer to take three or cycles to dry clothes with this problem.
The customer stated he had about 25′ of venting through the roof. This is almost by far the worst design for venting dryers.
Another problem common with roof terminations is the presence of the factory supplied animal guard on the termination.
The clothes dryer needs three factors to operate efficiently: movement, heat and a constant supply of FRESH air. Cleaning the dryer vent assures the latter in most cases. Failure to supply fresh air causes overheating inside the cabinet and can cause component failure, or worse, lead to a dryer fire!