I edited my previous post for a few possible solutions if you didn't see them but I've thought of some others you could try if those don't work.

You may also be swinging very shallow. That would explain the problem with longer clubs. It works with shorter ones but you bottom out to soon with longer ones. A good drill to try is get an alignment rod and stick it in the ground at the same angle as your shaft at address. Put it two feet outside of your right foot slightly under where your shaft is at address. Practice making down swings that come down above that rod and not hitting it. That will help your downswing be steeper and not as shallow.


You could also practice hitting balls on the range with both feet completely together. See if you still chunk it while making those swings. If you don't, feel the weight transfer and feel what happens with that and do it enough times you can repeat that in your normal stance swing.

Lastly, you may not be hinging your wrists enough in the swing, causing the club to bottom out sooner. At the top of your swing you could try hinging your wrists more and make sure you start your downswing with your body and not your hands. If this was the problem it'll actually give you more power. When you hinge your wrists more it delays the club from bottoming out and you might actually hit some shots thin.