Bone stock mill? High or low range? When it kicks is there any chips built up on the bit, whether packed in the flutes or on the lands themself? Is the bit coated, bright, black, makes a difference. It shouldnt have a problem drilling 3/4" alum. Drilling small holes in thick alum. can sometimes lead to chips not being removed from the flutes of the bit even with peck drilling. Speed sometimes doesent seem to help either. Without any coolant the heat on the bit can lead to the chips wanting to weld themselves to the bit especially right at the tip. Try running High Range just under half up on the dial and using WD40 or another light oil. Keep it shot to it pretty good, expecially after you start getting more that half through. When you retract from the peck look to see there are no chips still in the lands of the bit.