When you swing feel like your taking a half swing. It will feel weird for a while but its because your not used to normal swing length. Almost like your just hitting a chip shot.

If you don't have a coach and/or the ability to get a video to analyze your whole swing, you might be missing some else downstream, either an early wrist release or hips not clearing ahead of your swing due to overswinging.  I have a hard enough time evaluating my own footage without guessing something unseen.  I can certainly provide a lot of ways to leak distance - going past parallel is about the only one I haven't done.

Don't turn your hips as much. Everybody (including me 1 month ago) thinks that power is generated by swing speed. In a way, it is. People thinks this means a longer back swing for more time to generate swing speed. Torque is what creates swing speed. The long drive champion of the world has 41* of hip turn on the way back and 145* of shoulder turn.  Try to turn your hips as little as possible on your back swing and then fire them through on the downswing. This is the key to power and distance.

I had the same problem. I was into long driving for a while and thought "throw everything at the ball". Needless to say I didn't get far in LD, but still had fun turning my boxers around after each shot. 

Then, when I started getting serious about golf, and lowering my scores, my friend Kevin who is a PGA professional sorted my grip out, and taught me to not get past parallel as it created timing nightmares towards lower scoring. 

1st, he tied a long rope to my left wrist, and threw the tail end of it over my right shoulder and over a tree branch behind me. He told me to get into my golf setup, and then go to the top of my backswing. He pulled the rope so that there was a fair bit of tension in my left shoulder, but my left arm was straight. then he said the most important thing...

"Replicate that shoulder tension feeling in your golf swing, and you'll be set."

Every time I start getting past parallel, it is because I start trying to kill it... bending my left arm and getting "handsy" with it, instead of using the correct muscles to generate clubhead speed. 

Hope this helps 

This is what helps me a lot. When in the top of the swing, you should not see any part of the club in your pherphial vision. Maybe a little is okay but this works for me. Also keep your right arm straight at the top. Go buy some neon orange tape at the hardware store and put it on the topline of the club. Go hit some balls and concentrate on just barely seeing the orange at the top, or better yet see no orange. Hope this helps.