Brian,
Are you noticing any other symptoms with your irons? Ball flight too high, too low, hook, slice? If not, your probably casting your hands and releasing the club head too early.
Try this simple test. Turn you 4 iron upside down, grip it right below the head and take a normal swing with it. Really pretend you're doing it like you are at the course. Where do you hear the "wooosh"? It should be at the impact spot and extending through and after. If you hear it during your downswing and prior to the impact zone, you've expended all your energy prior to hitting the ball and robbed your swing of club head speed.
Seeing and instructor is the best way to fix this problem, but if you go to the range with a buddy, an iPad, and some beers. Film a few swing, watch them in slow-mo, the try to correct the problem. Rinse and repeat.
For me (and this isn't advise for you) I try to remember to keep my grip soft and to really extend my arms out and toward the target and not stop. A full follow-through is key for me to keep the "woosh" at the correct point.
If you watch people on the internet they'll harp on shaft lean and and downswing lag--which are both great for pro players--but those are difficult concepts for us regular folks to incorporate into our swings.
I hope you get it resolved. Not knowing what club to grab at what distance is not a recipe for stress-free golf.