2003 Chevy Tahoe Keep getting codes P0171 and P0174

You may have a vacuum leak, get a can of spray gumout, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs!
On yours with the plastic manifold, spray around the seams and the valves on the side, may need a new manifold or gasket.