Gregory,
What kind of bullet are you shooting? If I use a 180gr XTP with the same charge of powder the mv from my 10" barrel is down in the 1600s. A cast bullet will generally get more mv than a jacketed bullet with the same powder charge. I am shooting 180gr Laser Cast bullets. I have discovered that if I tumble lube them with Lee Liquod Alox, in addition to the hard blue lube they already have, I can cut the leading down to almost nothing.
There also may be some difference in chronographs. I have shot mine and a buddy's side-by-side and there was some difference but very little. You may want to check yours with someone elses and see if yours is registering low. Mine and the one I tested it with are both Chroneys so they may error the same.