I don't even OWN a 3 iron. How about getting a hybrid? Better yet, why not let me fit you for one when you see Lynn?
In the meantime, try to hit full shots at 1/2 your normal distance then gradually increase to 3/4 then full. Once you slip into a rut go back to 1/2 distance and proceed again.
To clarify, this means that if your 7 iron normally goes 160, then try taking full swings to an 80 yard flag and still feel compression.