POOR performance after ultra grate retrofit on Advantage

I have an Advantage II that I retrofitted with the ultragrate kit 3 months ago. Since then, I have had nothing but BAD performance. I cannot turn the auger past 2 without pellets building up and even on level 1, I have to stir the pellets around every few hours or they will build up in the grate. Also, there is a lot of black buildup in the box, on the window, and even the side of my house is now black. I have adjusted the damper from almost closed to ALL OF THE WAY OPEN, which is where it is now, and nothing seems to make a difference. I cleaned out the exhaust pipe at the time I did the retrofit including completely taking it OFF the stove and out of the wall to make sure it was very clean. Probably overkill, but I'm terrified of a chimney fire.

Any ideas as to what the problem is? I thought this grate was supposed to make it burn better, but I'm very disappointed to say the least. I'm ready to throw the old grate back in and be done with it! The flame is not lazy and it's not hard to light. There seems to be enough air getting in to burn, but not enough to burn the way it used to.

Thanks for any help!

My supplier did switch pellet brands this year, but I had used the new ones with the old grate and I still had a few bags of the pellets from last year left and tried those and it doesn't seem to be the pellets because it didn't make any difference either time.

The new ones are Pennington. The old ones are BioPlus. I would try the BioPlus in the grate again, but they are buried under about 45 new bags of Pennington now!

I took the whole thing apart today. What a job... and messy. But, I found that in the 3 months or so that I've been using these pellets, there has been enough fines spill out the bottom of the auger channel to completely clog the intake vent INSIDE the pellet stove. I have never had that happen with other pellets. So, it may be just a coincidence that it clogged about the same time I changed the grate out. Or the old firebox having a pipe that goes into that intake channel and past the flange may keep them from getting clogged more efficiently. Either way, there are apparently lots of problems with the Pennington pellets according to other posts. The stove is lit again and now I'm working on adjusting the damper to see if I can get it burning properly. I'm hoping that this has fixed the problem. It has to help at least SOME!

Of note, does anyone know why there isn't just a straight shot from the air intake pipe to the firebox rather than having the intake opening to the inside of the stove and then a second opening a few inches away to the channel into the firebox. It seems strange to engineer something that way.

Thanks everyone for your advice.