It sure sounds like your cat is about shot and lots of coals indicates wet wood.More details:
Big and old drafty house, center chimney with two 6" liners, about 25 feet tall. Dollar bill test shows a small spot near the handle that isn't as tight as it could be. I just tested a couple of pieces of room temp fresh split: 19.3% and 22.1%, so some of my wood is good and some is a little too wet.
I fill the stove, throw the bypass as soon as the cat probe reads active, let it run for a few minutes and then slowly start to turn the tstat down. Cat probe continues to go up until it about maxes out. I've set the tstat to 2, 1.5, 1, and lower than 1 (my tstat spins about 180* past 1??), All with the same 8-12 hour burn. By the end, I have a ton of coals but hardly any heat and the probe has dropped to inactive.