Im jumpin on the OS bandwagon as well. I hve two of the 55AX motors and love them. I did notice the midrange issue but it quickly went away after it broke in. Right now I have one in a EF Chinn Yak and it throws it all over the place. It is about to come out though because I am switching it to a Saito .82. I am putting the 55AX in my TH trainer. It is scary fast with the 55 in it. I use the tower Muffler as well and it is one mean sounding trainer.