about a year ago, i had a similar problem. It was actually during the spring, when i hadn't golfed for awhile. I went to the range, and i felt my swing was fine, but i would chunk all of my iron shots.
what helped me was: taking my time, and starting with my wedges, and 9 iron, and working my way up to my 5 and 4 irons. I hit about five decent shots with each club, and then work my way up.
my biggest mistake at the range, is going out and trying to kill all of my drives. sometimes, (especially if i am mad at something
) i will go out to the range, and just try to hit every ball as far as i can. That always ends up messing up my swing in the long run; even if i get a few nice crushers.