Shifting at 8500 is wayyyyy too much for these transmissions, you have to remember everything inside the trans probably spins at 3x that speed. The MP7A jdm transmission shifted at about 7600rpm on the SiR-G, thats about as high as I would want to go myself. Part of the reason I didnt buy cams that were pushing the power up that high in the RPM band. The input signal from the tach is what we modified to trick the trans computer to thinking that the engine is spinning slower then it actually is, that is what causes it to shift at a higher RPM without freaking the computer out, however beyond a 10% change I dont know how that would effect the drivability, remember, it effects all points on the shift range. I paid a buddy of mine 500 bucks to get all the work done on the head, including the PnP, milling, valve work, etc etc etc. But you can contact Pure Tuning I believe they do their basic PnP work for between 800-1000.