I have much the same problem you guys are encountering. My mast is stepped on a
steel plate that sits on a big lump of lead. The mast is also corroded due to the galvanic activity of dissimilar metals. I was advised to cut off the damaged portion of the mast and replace steel with
aluminum. I was also advised to make up the difference
lost with the plate, and insert a "filler" of aluminum fitting into the bottom of the mast. Not sure why I should use the filler, but it sounded like a good idea.
As for the Atomic 4, mine is not running yet, but I have heard/ read that the original
2 blade, 12" prop is inefficient and too large. Indigo and Moyer both make a
3 blade, 10" prop that increases performance. This may help your problem, but not really sure what gas mileage was in the first place...