Brad,

Two suggestions for getting your irons back on center.
1) Aim small.
Pick a spot the size of a BB at the center of the clubface and aim it at a single dimple on the ball. You can hold the ball and club up to your eye to see exactly where the club touches the ball at impact. As you address the ball you can see the BB spot and imagine the impact point on the ball. "Take dead aim" and keep an image of this aim in your mind from take away through impact.
2) Practice with half swings.
I agree with Billyg. Take a 5-iron and hit shots at the 100-yard sign. Work on precision and timing rather than power. If you find a swing fault it is easier to fix at half-power.
IMHO there may be a "hitch" somewhere in your full swing that is throwing off your aim. Maybe your grip loosens or tightens at the top. Most probably your body turn is ahead of your arm swing and you are blocking it out. The timing with your wood swing can easily be very different from your iron swing. I think we all struggle with that.
Doug