Jett props
I have Sport Jett 50 with a Jett Q40 pipe on my DD. I tached it at 19,000 peak on an APC 8.75x9.0W pylon prop. When I richened it up fly (I am not to going to take off at peak rpm), it would not quite get on pipe, so I dropped to an APC 8.75x.8.5NN. It really likes that prop. I haven't tached it but the way it hops in the pipe in the air, I am sure its around 19,000 rich on the ground.
Your engine may be getting tired, but you should try a little less prop before sending it, such as an APC 8.75x9.0, or 8.8x9.0. Performance Specialties stocks the 8.8 sizes for the Nelson Quickies. My local hobby shop orders the 8.75 sizes for me. I just got an 8.8x9.25, but I haven't tried it yet. I will probably cut it down a little.
The APC pylon props have the thick hubs. I would not trust APC sport props at these rpm's.
Paul