A while back, I had a problem with my dryer that when serviced, a flexible attachments was installed. It looked like metal but wasn't and the air flow was somewhat restricted as it was not a direct path to the outside of my condo.
I had to have it redone and a rigid metal attacment was installed with metal taping. I had a vent hole installed as it was a much shorter route to the outside world. No problems since.
BTW - if one's clothes are damp after drying, it is a very good indication that vent hole is clogged and requires immediate attention. Unfortuately, I'm not too bright as it blew the dryers fuses twice.
I aslo clean my dryer's lint trap after each use.
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"It doesn't cost "nuttin", to be nice". 
MOM
I just want to do the right thing! Uncle Joe, (my hero).