If your head is milled anymore than .012", it is most likely your cam timing. For every 12 thousands of an inch milled, it will retard your cam timing by 1 degree. I repeat, you will need to compensate your cam timing if your head is milled unless it's really minute...then again, if it's that minimal, your compression wouldn't be so high.

Just curious, did you guys open up the valve reliefs on your stock pistons at all? The reason I ask is because with your head being milled and all, may cause piston-to-valve contact (also depending how much was taken off the head).