P0171 Trouble Code

Hello All. I need to get some help with this code. Any suggestions? I have a 99 GP, 3.8 K-vin, 91,500 miles; just changed the head gaskets up.

DTC P0171 indicates the system is in a lean trim mode. Ideal fuel trim = zero. Greater than zero indicates the PCM is adding fuel to compensate for the lean condition. If fuel trim is less than zero the PCM is reducing the amount of fuel to compensate for a rich condition.

Here is the course of action per the GP GM service manual:

Check all vacuum hoses at intake system.
PCV Valve
Possible throttle body blockage (clean input screen and body)
IAC (idle air controller valve)
Check fuel injectors (bad o-ring seal)
MAF sensor
EGR valve
Check 02 sensor