[Barnsnake]

I would expect a pulley ratio issue to manifest itself at a lower rpm.
It might still be instrumentation. As Cowtown noted the temperature gauge may be subject to variations in voltage. If you have a voltmeter, it might be interesting to note any change in system voltage around 2000-2900 rpm.
Also try downshifting to bring up the revs while operating at the same speed. This will tell you if it's RPM or air flow related.
Please verify that gauge and sender before beating your brains out on this.