I had a similar issue with my Bach 37, it seemed harder to play above and below the staff. I tried 3 other Bach's, two 37's one 43/72 and none of them had the same problem. They all seemed easier to play than mine. I tried different backbores and it didn't seem to make it any better. I started looking for other horns and tried a few different brands and ended up getting a ZeuS. It plays great in all registers. It plays and sounds better with a tighter backbore on the mouthpiece than the Bach. Maybe a valve job would help my Bach but I will probably just sell it.