The symptoms do suggest stuck slide, and I thought that you cannot even screw on the cap to close the tower if the tab isn't aligned with the slot in the slide tower.
I believe what you are saying, the only thing I can think of causing high idle is the slide not closing all the way.
I don't think an air leak or airscrew could cause a high idle. You jetting seems in the ball park, certainly the pilot (#40). Maybe, just maybe try a #42 ??
I've gotta vote with Jerry on the slide though. It's the elephant in the room
