XL,
A vacuum leak would have to be really severe to cause missing at higher RPM ranges. Any leak that bad would probably cause serious idle problems, like not letting the engine idle at all.
It's more likely the ignition system. Start with the basics, like cap and rotor, test the plug wires, install clean plugs, test the coil, pickup, HEI amplifier, etc.
It is also possible that you have a compression or valve sealing problem on a cylinder, or a fouling injector. Since the engine is apparently new, the compression and valve sealing should be ideal. If the injectors were not new, and were not serviced when the TPI was installed, the spray patterns and/or flows of the injectors may not be satisfactory.
I chased a similar problem on my TA for a couple of seasons, and refused to believe the injectors were a problem since they had been "professionally cleaned". I finally eliminated everything else, pulled the injectors again and sent them to
Cruzin' Performance. I got an initial flow report, and progress report along the way.
Even though my injectors were cleaned and passed the resistance test, the flows were off by almost 20%. Eighty bucks later the car felt like it had a new engine. I guess I found out who the real professionals are.
Just a possibility if you eliminate everything else.
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Later,
Vader
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"
No matter how hard you try you can't stop us now"
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