Mud, what you need to do is get a manometer (Google it, they are cheap) and drill the hole between the stove and the MPD. I try to maintain about .05" of draft at that point. I also have a barometric damper in the stovepipe, I have a triple wall metallic chimney and it is a vacuum cleaner once warmed up! Excessive draft will throw all of your heat up the chimney, and I suspect that is your problem. Don't be afraid to close the MPD all the way.. Close it, give the stove a minute or three to stabilize, then slowly crack the loading door, if it sucks air in, you have enough draft to send the combustion gases up the chimney. It may be too much, or it may vary depending on chimney temp, wind, etc. Get a draft guage and do it right, it will save you a lot of coal and will keep you safe as well.
Ops (retired burner mechanic, plumber and AC man)
ETA: nice scoot..