Hello, and welcome to JA!!! codes PO171 and PO174 indicates both banks are running lean. the two most common problems for these codes are a weak fuel pump, or a intake gasket leaking vac. if the vehicle starts ok, the normally the fuel pump is ok. more than likely the intake gasket will need to be replaced. let me now if you need any further info on this concern.
: Cold Engine Idle Misfire Or DTCs P0171 P0174 - keywords 4.8 5.3 6.0 air cold crack hesitate idle intermittent internal intake leak lean misfire miss P0171 P0174 P0300 power rough surge vacuum
99 through 05 GEN III truck engines may experience any of the following:
A cold rough idle that diminishes as the engine warms up.
Possible DTCS P0171, P0174, or P0300.
Random misfires at idle.
The intake gasket seals may be leaking around the intake ports, causing a lean condition. The intake gasket seals may leak around the bottom side of the port, making it a challenge to detect the vacuum leak. The technician may also notice lower than normal MAF readings if the intake seals are leaking.
If leaking intake gasket seals are found, replace the intake gaskets. During the repair be sure to use the current GMSPO part number for replacement intake gaskets. The current GMSPO part number for intake gaskets will have a teal green intake gasket seal. The old version of the intake gaskets were orange in color. Use only the teal green colored gaskets for a repair.
fairly easy repair, if you have some mechanical skills, should be able to handle. takes a couple of hours to do.
here are the instructions.
Intake Manifold Replacement Removal Procedure
Important: The intake manifold, throttle body, fuel rail, and injectors may be removed as an assembly. If not servicing the individual components, remove the manifold as a complete assembly.