Since your stove is fairly old, the top of your door probably doesn't have any gasket so the airwash works to keep the glass clean, hence you don't do a dollar bill test up there.Pellets are north Idaho energy pellets. Best I've had so far and I've tried about 7 brands before burning 3pallets last year and almost a pallet this year before the problems started. After I made my initial post I pulled the burn pot out an it is free of ash and obstruction. I haven't had a clinker since I started using these pellets. Just did the dollar bill test on the door. Bottom 3 sides I can't pull it out, as well as the far right side. top and far left it pulls out with minimal effort. Maybe that's the problem. Just pulled the entire stove out and disconnected the vent/chimney pipe, clear maybe 3 tablespoons of ash at the elbow. Trap door clear as well.
You don't say if you've ever had your combustion blower out for a thorough cleaning of the impellers and the chamber itself. Also, you had the burn pot out but didn't say if all those holes and the slit are clear. Is the dump valve on the bottom tight enough? It should not be sagging down. When you put the burn pot back in, did you use a new gasket?
What is your exhaust system like? Out the side or up?