Older Quadra Fire running out of air when damper is closed

[I love winter]

I have a mid-80's Quadra Fire 4100 freestanding wood stove that just began acting up. I have replaced and or cleaned everything I can reach or see, including the chimney/stovepipe/topper/stove lid under the stovepipe (cleaned), replaced the stove brick, door gasket and shop vac'd everywhere the hose will reach, the fire goes out when the front - main - damper is closed all the way. There are 2 dampers, they both operate smoothly and easily. The stove has two air pipes that exit from the back of the stove box, these both look clean and open. I burn mainly ponderosa pine and don't close the damper until the stove is well heated up, but for the last couple of months have resorted to leaving the damper only partially closed, as no matter how well it is burning, it goes out within a few minutes if I pull the lever all the way out. Any ideas out there?
Thank you so much!
Has anyone out there ever 'backblown' the dampers? I am wondering if there is just a small blockage somewhere and it might dislodge or unplug if blown from a different direction from the air intake. Any thoughts? Or, any success or experience in trying this?
Thanks!

 

[Rickb]

Is this stove new to you? Has it ever worked differently then this?

 

[I love winter]

Not new for me, new behavior for the last couple of months. Thanks!

 

[moresnow]

Have you started burning different wood? Sounds like its possibly wet.

 

[I love winter]

No, the same well-seasoned dry wood, no changes. Starts and burns same as always right until I close the damper all the way.