My only guess on the tach could be that the signal wire is getting electrical "noise" from the ignition system past 5K... maybe try running some shielded wire for the tach signal? I dunno man... I'm def. not the guy to ask, but that's my $.02.
![tongue.gif](style_emoticons/default/tongue.gif)
Other than that the car sounds great man! Feel a power difference over the ole' EW?