Newbie: 2004 GMC Sierra P0650/P0496 Oil Pressure Gauge Malfunction?

[NastyBuzzard]

Just traded my 99 Z28 NBM 6speed convertible for this truck.

2004 GMC Sierra Crew Cab Short Bed Z85. Truck has 128XXX miles on the body but dealer replaced engine at 78XXX. 5.3/4L60E 3.42 peg leg..

Pics are from the previous owner, I haven't cleaned it up yet for pics.

















It has a couple issues.

Has codes:
P0650 MIL Fault?
P0496 unwanted vacuum? Bad purge solenoid?

To start with the engine oil pressure gauge is acting crazy. With ign on, eng off the gauge pegs to 80. When you crank engine it pegs to 80 and sometimes will stay at 80 or drop all the way down to 0. Any ideas if its oil pressure sending unit or stepper motor in the cluster?

Previous owner said that when he fills up the truck and goes to leave station the truck is hard to crank for a few seconds but will eventually start. Starts fine all other times.

Any ideas fellas? Other than needing new tires (tires for 20" rims are expensive as hell!!), the truck seems great! Eng/trans is so clean you could eat off of it!!

Also thinking of getting rid of the step bars and the bed rails, maybe even the bug shield. Thoughts?