According to what I just read...the only change was the tune. I would start there. "So everything was running fine for a few 100 miles, then I shipped the car to Denver. Where was the car running fine before you shipped the car to the "new elevation? The elevation will affect the tune....but it won't cause it to quit at 3-4k rpms... That could be the tune. Remember when you rev, it is limited to those rpms so not to damage the motor. Fuel pressure is holding steady, which it is supposed to do. Now, are you running a 61 or 62 pulley? If you are, you may not have enough pump. That is a big if though...as it should still run better until it runs lien and falls on it's face. PM me and we will talk.