bad vibration in entire frame

[rk4g63]

Super4X4duty / 1quick4,
I tried pressing in the clutch at high speed - at 80, at 70 and at 60 on different occasions. When I depress the clutch, the vibration goes away - BUT, I am not accelerating in this instance. In another instance, when I depress the clutch and accelerate at the same time to maintain engine rpms, the vibration/buzzing comes back.

Gotta specify - its a buzzing type of vibration.

Its more significant at higher speed. I've been doing 80 often since I bought the car, so its more nociceable than everyday driving, unless I'm accelerating hard in the city - the buzz/vibration comes back. Its all Kenny's fault because he had a damn nice car!

I have to specify too - the car does not shake as a whole as a rewsult of the vibration - it buzzes annoyingly in teh dash, center console and A-pillar and vibrates those areas.
Seems to be both rpm as well as speed sensitive.