Seems lately I've developed a bad habit of not following through completely. Cutting my swing short and inside creating a terrible slice on all my irons. Bad thing is I know I do it but yet I can't stop it.
It's probably not your follow through, but instead your backswing puts you in a position to come down outside and finish inside.
1. Go to a mirror and check to see at the top of your backswing if your right elbow is flying out (pointing your club diagonally to the right of your target line). If so try taking the club out 'wider' in the first portion of your swing and hit a few 3/4 shots too see if that corrects it.
2. It could also be swinging too hard from the top causing you to cast out the club over the line. Focus on clearing out your hips more instead of swing down with the arms in the downswing.
3. You could be "losing the club at the top". For a test, put a tee sticking out on top of the grip and address the ball with the tee placed between the pad of your left hand and the grip - sticking out off the end of the club. If you swing to the top your grip loosens up too much the tee will fall out. the result is you regripping the club on the downswing causing a cast outside the line. Grip the club tighter in the 3 fingers in the left hand and work on the tee drill until it feels comfortable enough where you don't drop the tee at all.
You probably cut your follow through short in an effort to guide the ball. In reality at impact your club comes from such an outside path there really is no good move after the swing to compensate for the slice.
btw, these are just 3 possibilities and 3 drills. I have MANY more fixes for an outside in swingpath, but this is a good start. Also, don't try all these drills if you don't have too. Find the cause and only work on that fix - not all 3... if possible.