I have a 1998 GMC K1500 Z71 offroad with the Vortec 5.7L 350ci V8. Purchased in Kelowna, BC in October 2013 at 157,000kms (98,000mi). Currently has 164,000km (102,500mi). Cold air intake True dual exhaust (no cats, dual in/single out Magnaflow muffler) Nothing else done to the engine this far. Idle is 600RPM, my oil pressure fluxuates from nearly 0 at idle and back to normal (275kPa/40PSI) at WOT. Oil Pressure is perfectly fine when engine is cold, but once it gets to operating temp the oil pressure starts fluxuating insanely. Not sure why this is happening, started happening more after the exhaust was done (cats removed). Never burned oil until today (April 12, 2014). Started burning oil for about 5mins, then stopped and hasn't since. NEED HELP!!! This is my only vehicle and I am going to university right now so don't have enough money or time to fix major repairs. I'm hoping it is something cheap and simple! CEL/MIL is on for O2 Sensor since cats were removed but getting an O2 Simulator to eliminate that issue. At this point my thoughts are: Oil pressure sending unit Oil Pump Oil pump pickup screen/tube PLEASE POST ANY SUGGESTIONS AND/OR EXPERIENCES OF THIS PROBLEM AND HOW IT WAS REPAIRED!