Sheesh, it's all perfectly clear now! Have you checked for a Santa stuck in the flue? Perhaps, as others suggested, there's an air leak. On my Intrepid, there's a spot near the back right corner where the tie rod goes through the firebox floor .... the furnace cement tends to fall out. You can then see daylight out through the primary air vent from inside the firebox. Perhaps a similar situation exists on your stove that's allowing uncontrolled air into the firebox? Recheck your assumptions about which seals/gaskets are good....check 'em all again. Good luck.