The Titleist site highlights the new designs of the 913.  Lower CG and hotter face are the two main ones.  Without seeing your grip or swing, their could be a few variables in the shaft.  The Ahina 72 stiff has a HIGH kick point, 2.7 deg of torque, and a weight of 71grams.  The D+ has a HIGH kick point, 3.3 deg of torque, and a weight of 74grams. 

Here is a publication that has some information too:

http://media.titleist.com/images/titleist/pdfs/US/2013/2013_Custom_Options_Book_US/html/index.html#4

Thanks Brent

Anyone on here own both? I'm thinking of upgrading my 910d3 at the end of the season. 

I upgraded my 910 D3 to the 913 D3. Same shaft. +15 yards, mishits are longer and straighter.

Mark That seemed to be the case for me as well. Now the problem is can I afford the cost for 15 yards.

Austin,

I went back and forth and talked with my golf buddies. Ultimately I bought the 913. My score was lowered 2-3 strokes. I play to 17-20 handicap. I am closer to the green ( at least 1 club if not 2) and my misses are generally playable. I can style miss hit it. Where I really notice the difference are the long par 4s.

Mark

Josh, 

 I have them both and the 913D3 is more forgiving and length for me is about the same.  Feel is a bit better with the 910 in my opinion, but the 913 flight control is nice.  A bunch of variables to consider.  I would not have switched had I not gotten a really great price on the 913.  And I transferred my AD DI 7X into the new head.

TT

What I was referring to was the grip size Brent. I have a mid-size grip on my 910.  The demo club had a standard grip

It looks like the newer shaft was too high of torque for you as the D+72 was 3.3 and Ahina was 2.7. This could be why you were missing it to the left as well with the grip size.

I really don't think that was the case. The grip is too small and I felt like I had to grip it tighter than I like.