I have a 5.3 V8 with a check engine light (P0171 - "Fuel System too Lean").

(5.3L) .. Rough idle only on cold engine start up?.... Idle smooth out after engine warms up or reaches normal operating temperature??

copy and paste the link.check the engine area for vacuum leaks first.could be one or more of the things listed.unless you can find it,the only real way is a scan tool with live data.......... P0171 Chevrolet - AutoCodes.com www.autocodes.com/p0171_chevrolet.html

could be ur intake gasket, has a rough idle at first, then when gasket swells w more heat, it idles smooth. gm known for using thin gaskets.