Sad panda time. I can't figure this out and have been chasing it since the engine came out and went in this fall. This problem *had been* intermittent, but it seems to be more frequent now. Symptoms: The tach starts jumping around and the engine speed changes (note oil pressure gauge as well). The big revs are my right foot. The following has been done:
- tested plug wires (february)
- tested battery (this week)
- tested alternator/VR (this week)
- checked grounds and all
- test for air leaks (December, Matt deMaria, March, GAG)
All those electrical things can't account for the rise in engine speed...it's almost as if it is taking in more air somehow...I can't make any sense of this.
Guess from you are probably better than my guesses at this point.
Maybe Crazy Ray's can fix it. 
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