Ball flight issue

I am new to the OPS and this site.  I have been working on the fundamentals that CQ talks about on a daily basis.  Everything seems to work fine until I get to the 5, 4 and 3 iron.  On my longer irons the ball starts low, straight and penetrating then it starts to tail off to the right (about 10 to 12 paces on a 4 iron shot 200yds) after it reaches its apex.  I still have good compression of the golf ball with these longer irons.  I know this could be an over the top move, but the ball seems to start on its intended target line and not left of it.  I find that I have to really concentrate on my weight transfer and hip turn to get the ball to stay straight and true.  However, this slows my swing flow and my misses are a little fat.  Has anyone else had this problem and found a solution or is it just me?  Any insight you all might have would be great.