P0171 DTC - sys too lean (Bank 1)

[cmart]

1999 Chevy 5.3L Auto with 150,000 or so miles. I've noticed it missing a little for a while and just figured it was time to do plugs and wires, so I wasn't too worried about. The check engine light is starting to come on and it will go off after a while. I finally got my hands on a scan tool when the light was on and it showed the P0171 code.

I know that this can mean a vacuum leak, MAF dirty or bad, fuel filter dirty, etc. My question is...what do you all think I should address first in trying to figure it out. Is there one thing that outweighs the rest when it comes to this?

Any information would be appreciated. Thanks in advance.

Cory