RE: slugs shooting high help!!
Does your shotgun have adjustable sights? If so is the rear sight in its lowest position? Are you resting the barrel on a sandbag when shooting instead of correctly resting the forearm of the stock?
I'm just speculating, since I don't have much experience with slug shooting, but from experience with handguns and rifles but I would guess that at a short range a heavier slug would shoot higher. The heavier slug takes more time to travel down the barrel so that the muzzle has moved upward more from recoil by the time it exits versus a lighter faster projectile.
Alcohol, Tobacco, and Firearms... who's bringing the chips?