[mastersat1]

If this is a vortec, I would check into the cpi unit. It's often called a spider injection assembly and is located in the upper intake. When u check the fuel pressure with engine off does it hold for 5 minutes? If not, the fuel regulator diaghram could be bad. This should be obd II, does scanner register any misfires? You also need to unplug connector on top of intake and check resistance on all 6 injectors and check to make sure all injectors are receiving a signal. You can do this with a noid light or a dvom.