Engine Vibration - 3K RPM

[SSL]

I'm having a engine vibration at 3000 RPM and haven't been able to diagnose the problem. After about 300 miles of use, the vibration started and seems to be engine related.

Drivetrain Details:
- ZZ502, Fluidamper, Holley 850, MSD Digital6, March serpentine with AC
- T-56, Centerforce DF, Scattershield (indexed)
- Hydroboost brakes

Items looked at so far:
- Vibration occurs when:
- Moving and sitting still
- Clutch engaged or disengaged
- Trans in gear and out of gear

- Plugs and wires checked - plugs clean, gap correct
- Replaced waterpump

Any ideas on what to look at next?

Thanks,
Steve