im sure it's not the vacuum system at this point. can the bowden cable effect shift hardness? i adjusted all my linkage so the "arm" on my IP hits the stop when my foot is to the floor and i noticed that at WOT it would only shift at 3000 rpm, so i backed the plastic bolt out a bit until it shift around 4200 rpm WOT. when your easy on it, it will shift at 1400 rpm.