Also, since you posted in the winter---though I don't know where you have been playing---I'm guessing that temps may be a bit cooler than your typical in-season round. Expect a 10 yard drop in distance when the temps are below 55 or so. Just something to consider, if you haven't already. Particularly at sea-level. Again, I have no idea if you are playing in cooler temps, or at sea level, so I am only offering this reply based on my speculating that this might be the case. Just a thought.

I'm a pretty big believer in this. When I made the switch to my new AP2's I have noticed I actually lost about 5-7 yards per club. Given that I live in Michigan and do not really have the opportunity to play frequently over the winter unless I travel or find a simulator. We have thus far had one day over 55 this year, so I am attributing the distance loss to the temperatures at the moment. 

Now, I do have a different shaft setup to allow for a higher ball flight, which can also take down some of the distance if there are any other external factors (wind, rain, etc.,) but generally with the AP2's I should be hitting the ball further, if not the same. 

The best drill I know of is on the range, practice swing at slow motion, practice swing at normal speed, practice swing as fast as you possibly can.  Now hit a shot at what you think is normal speed.  Do this drill about five times than hit the course.  Your swing speed will be up and you should hit it a little bit farther. 

Hey Michael,

I agree with Carl.  It could be age related.  Loosing flexibility and thus width in the swing is a huge power loss.  Another possibility is that you have over time become more of an armsy swinger, perhaps even coming over the top (starting down with the upper body).  I would try to get a full turn going back, with your weight mostly on the inside of your right leg and, if you are physically capable, try to turn your left shoulder under your chin at the top of the backswing.  From there, try to feel as if your lower body starts and leads the swing from the top.  The faster the legs and body turn, the more clubhead speed, and thus distance.  Of course, this is just my advice; it's impossible to fix your swing without being able to see it.  I just thought I'd share because the same thing happened to me last year, as I gradually lost distance throughout the season.  As Carl said, though, there's always the club pros that can evaluate your swing and find a cure.

Hope this helps,

Sam

Gotta hit down on the ball. Make sure you have width throughout the golf swing.