I've always had the luxury of being a NG consumer and yet I've burned for 20 years now. I just upgraded my heating system in my home to a triangle tube condensating boiler with FHW baseboards. NG is so reasonable I think I'll be cutting my pellet usage by more than 50%.
You're on the right track. Empty the hopper and look down through the slide plate and see if something is jammed in that way. As stated before, when was the last time you emptied the fines box? You can take the auger motor off fairly easily if you are handy. Start with this and let us know how...
Don't rely on that surge protector in your panel or the strips to protect your stove. Been there done that. You should get real surge protector and install it on the outlet your stove is plugged into. Many of us use one of these. https://www.amazon.com/gp/product/B00006B81D/?tag=hearthamazon-20
Given what you have described I would consider adding the heat option to your existing system. Doesn't sound like you got good advice on how cold it can get during a Ct winter. Do you have natural gas on your street? If not, propane or oil are options. Find a good HVAC contractor and go from...
You are going completely off the reservation by even considering a damper on the intake of a Harman. The stove is pretty "smart" even if it is an older one. Once you know how to operate it properly and you understand the feed rate, you'll get everything you want and more out of it.
I welded mine in my Harman Invincible but I disassembled the stove first. (big job). I would be very concerned about the circuitry in the control board if you are going to weld the auger tube while it is still installed in the stove.
If the above is the case, then something is very wrong!! You should be able to turn the stove to off and the combustion blower will continue to run until the flame goes out and the stove will cool down. This could easily take 30 minutes (or longer)
If you run the stove in Stove Temp mode, feed rate 4, and turn it all the way up you should have a rip roaring flame. If you don't, something is still wrong. I seem to remember someone with this issue a couple of years ago here but I can't remember. Keep us informed after different pellets.