Howdee all.
I have a refurbished whirlpool dryer that I bought from an appliance store back in December 2006.
My reason for posting today is that we've been having drying problems with it since within a few months after having purchased it.
In 2007, I climbed underneath the house and disassembled the dryer vent pipe, and pulled a good cubic foot of lint out of the pipe. I.e., the pipe was all but totally clogged.And there was enough air flow to lift the backdraft/rodent prevention flap.

The house of now 10 years old, and when it was built, I made an inline, wall-placed dryer lint cleanout box to ensure that the lint would not build up in the pipe-- use to be a sheet metal mechanic, and have had lots and lots of experience with this kind of thing dating back to mid 80's.
This past summer, I built a larger, inline cleanout "plenum" with a blue AC washable filter, and an access service door to get to the filter. 3 ft long, 12" x 16" with top flat square to round adaptors.

My schedule for cleaning out the underfloor lint box/plenum is every 3-4 months.
It appears that no matter how frequently I clean out the boxes, we have to still dry the clothes for 3 or 4 cycles because they don't get dry enough-- still moist and damp.

I wanted to start here so I could get some idea on how to deal with this drying issue.
I told you about the dryer vent line because I'm aware of the issue due to my own history in the trades.

We appear to be getting decent air flow at the outside vent opening, but drying sucks.

Your helps are appreciated.
Thank you.
Best.