Hi, i have a 2000 checy for vin c3500HD with 6.5l Turbo. I have replaced vacuum pump, pulleys, radiator/ oil cool / lines etc etc. Basically bullet proofed it. The issue i am having is that the vehicle has a weird vibration at idle and usually when im stopped at lights. As soon as im giving it throttle it goes away

When I release the throttle I will get a small growl / vibration that goes away immediately and the engine is very nicr / quiet until i get close to stopping, then when im stopped the vibration starts again.

When im driving it (applying throttle) it sounds great.

I am thinking air in the fuel lines?

Vacuum pump causing a vibration? (The vacuum pump and pulley were replaced a week ago. The pulley appears to wobble but everything else is fine. If I seat the pulley deep enough in the vacuum pump then it will stsrt to eat serpentine belts.. it functions great (wastegate wise - no egr on this vehicle.)

I am just looking for some help / pointed in the right direction of where go stsrt to get the vibration handled.

Any input is appreciated, thanks!