Pattern your gun to see that it is doing with the load/choke combination. IMHO 3's should be the minimum shot size for waterfowl in steel. Keep shots 40 yards and under.
If that doesn't work spend some time on a skeet field and work on your shotgunning. My first experince with steel was in 1976 and originally it was horrible but around 1982 or so Winchester Super X had it right and never had problems after that. In 3 or 2's it killed everything over the decoys cleanly from teal to geese.