Not sure if this is the right forum...

But here's my problem.  I have a good knowledge of opening play principles and play a strong positional game.  However, I can't ever seem to capitalize once I start reaching the point of when I need to attack.  I just kind of build up a strong opening and get lost after that.  What kind of training should I go about doing to develop the transition from the opening game to the end game. 

Have you tried Chess Mentor or Tactics Trainer?

http://www.chess.com/chessmentor/myhome.html

http://www.chess.com/tactics/myhome.html

In every game you should look for weaknesses or opportunities.
However small they may seem, you are always building up to that specific purpose, which can turn out to be a whole different one.
In the opening, there are scarcely any mistakes or strange moves, so it is important to gain your advantage there by focussing your moves to one purpose or area. This can be in a very subtle far fetched way. 
If there is an open line for example, or a castling on a side here you have much pressure already, or a spot that isn't looked after properly, find out how to take that spot. Once you have your setup, which is hardly ever good in a general way, there is always, or there should always be a purpose.
Calculate whether it is possible to gain your advantage in pieces or pressure due to position. Pieces are easily won by tricks, (fork etc.) so always look out for those. A more responsible way is by over pressuring specific pieces or areas.

So try to turn your positional advantage in an actual advantage by breaking up pawn formations, adding pressure to pieces or squares, or winning pieces.

Most important is there is a purpose to your moves, it doesn't matter if it is possible.