It sounds as if your 1/2 inch drill needs to be sharpened. You can
sharpen a 1/2 inch drill yourself on a bench grinder. Google on this
use group to find lots of discussion on sharpening drills.

If I were making slots by hand, I would drill a hole at each end and
another hole that slightly overlaps one of the end holes. Then I would
use a hack saw to saw the slots. and a file to get the sides straight.
A sawzall and a jig saw tend to bind and shake. At least when I try
using them.

Dan