There are two important things to check before you spend the money & effort replacing the pump assy.
1. Check for 12v on the grey wire at the fuel pump wiring connector coming from the chassis. This voltage should be present for 2 secs when the key is turned to the "run" position.
2. Check for a good ground signal on the black wire at the same connector.
If both of these turn out good then most likely the pump is shot. I strongly urge you to do these 2 steps before proceeding.
The link below has about the best prices on OEM stuff. You'll need to send them a message with your VIN to get the correct part number.
http://www.gmpartsdirect.com/ Click on the "customer service" link.