Are these bad pellets?

[my2bads]

Hi. I have been periodically reading these boards for quite a while now and I hope someone here can help me out. This is my third season with my Whitfield Profile 30 FS-2, which I bought new and run on a thermostat. For the past 2 seasons, I have been using premium hardwood pellets from Lowe's - Clean Energy brand. They ran OK for the first year, although sometimes they would get stuck in the auger as they were too long. At this point, I was having to clean out the ash about every 1 1/2 to 2 days. The next year, I was using the leftovers from year one, which seemed to have accumulated some moisture and didn't run as well. The amount of ash almost doubled and they didn't put out near as much heat. Now, with the length issue of those pellets, I switched to Pennington's Nature's Heat brand premium hardwood pellets from Wal-Mart this year. These pellets definitely give off a lot more heat and VERY little ash, which is more black instead of the previous brown. My problem here is that every fourth run or so, the grate will get about 1/4 inch of a what we believe to be carbon buildup in the bottom that blocks the airflow and causes the pellets to overrun the burn pot. I thought that maybe it was an airflow problem, so I tore apart the stove and gave it an extremely thorough cleaning - motors, air inlets, exhaust, etc. I have tried setting the damper everywhere from nearly closed to wide open, and it still happens. I have checked the pellets for moisture - they're fine. I had also read on here that if they still smell like wood, they should be OK - and they do. Oh, there is not a lot of buildup on the glass, either. Am I missing something here or are they just bad pellets? If so, can you return pellets? If not, it will be a very long season!