It's impossible to say without seeing you shoot, but most people I've helped with 1 & 5 had improper foot position. You might try this. Let's use station 5 as an example. Stand with your gun mounted so that you are in a comfortable position to break a hard right bird. Then, rotate your body and gun back to your hold point before calling for the bird. Your body will then be set to swing to a hard right angle. You may be standing so that your body stops swinging on hard angles because it is positioned in such a manner that it "binds" before swinging all the way through the bird. Do the same on station 1, but position yourself for a hard left bird and then rotate your body and gun back to your hold point before calling for the bird. Same theory applies. Once you determine your needed foot position you will not need to go through the motions any longer. However, I know shootrs who have been shooting many years who still do this for every bird on 1 & 5.
I also agree that a round of skeet from time to time will help, and remember that it is much easier to shoot behind the bird than it is to shoot in front of it. A good rule of thumb is to lead it the amount you think is right and then add about 1 foot for hard angles. That works in skeet on stations 3, 4, & 5, too.
Shoot well and often,
Mark.