My oil gauge is sittin on 0. It will move back up to 20 or so.

Assuming you have the correct oil weight and you change your oil on a regular basis, I would start by inspecting the oil sending unit for any loose connections. It's also possible that you got a defective oil filter even though it's new.

return and ask questions about last service. also as stated poss oil sending unit wiring or sender itself

If no problem with the sending unit, have a mechanic check the actual oil pressure with a test gauge. Then you will know for sure if a pressure problem exist! Does the engine make any strange noise? Some of the 5.3 & 6.0 Vortec engines 'had' a problem with the oil pickup tube assembly. (Fact)