In this case, calm is your friend. Okay, you may have sucked some junk into the High Pressure Fuel Pump or pressure regulator/damper, or the HPFP may have bit the dust.
When my HPFP had problems, the symptoms were:
* Misfire then sudden loss of power.
* Would not build boost, max RPMs while accelerating were 3,000 RPM.
* DIC indicated "Reduced Power
I limped home at no faster than 50 MPH and immediately hooked up my inexpensive scan tool.
According to the scanner, I had low secondary fuel pressure.
A couple days later, I ordered from GMPartsDirect.com a new HPFP, Fuel Damper and High Pressure Fuel Line. Rob from this forum suggested I go with Crate Engine Depot and I'm sure they're fine. I just couldn't find the part on their website, but could at GMPartsDirect.com. I paid about $229 for the pump. (Stealership wanted almost $600)
If this is the same issue for you, I suggest you replace the fuel damper that goes in front of the HPFP and absolutely replace the high pressure fuel like that runs between the HPFP and the fuel rail on the side of the engine. That way you don't ingest water and junk that may be caught in the damper into your nice new HPFP. The HPfuel line uses crush fitting which are meant for a one time tightening. Trying to reuse the line could cause a leak and air into the fuel rail, so should you replace the HPFP, replace the line too.
Replacing the pump is pretty straight forward. The pump is on the drivers side rear of the engine. There is a silver metal fuel line with a straw hat shaped piece in the middle. This line is the low pressure feed line that goes into the HPFP. All you need to is open the hood, remove the windshield wipers, pop off the plastic "Ecotec" engine cover, remove the screws and push-in plastic rivets that hold the big blastic tray under the windshield. Once you remove the tray, you'll have pretty good access to get a 10mm 1/4" socket and wrench behind the engine to remove the pump cover (black powder coated metal cover). Once you get in there without the pump cover, you'll see how things come apart.
One thing to be careful about when reinserting the new pump: Since the camshaft drives this pump, make sure the pump plunger fits smoothly into the pump and the plunger into the cylinder on the head. It is a very precision-machine part that only fits on one way. Lubricate the plunger with new clean Mobil1 5-30 before fitting it all back together. Do not force anything.
Good luck!