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

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)