Does anyone know exactly how I can troubleshhot the problems with these codes. I've already changed the gas cap after Autozone said the PO442 code showed up. A day later the light came back on. Replaced fuel cap again with no success in keeping the check engine light off. Then Autozone said there was a small leak and a big leak in the evaporative emissions system. These are the codes they pulled up today. I have a print-out from Auto Zone with very brief details on what the codes mean.

Does anyone know what I need to check or replace?

AutoZone was incorrect. The codes stand for a leak in the evaporative system. Best thing to do is take it to a dealer or a trusted mechanic. The tubing can get extensive. You may want to look at a Tee connector next to the evaporater (Black can on left side of engine) these sometimes erode.

The evap system is located on the left side under the hood ( standing in front facing engine) there are several small components to it and several vaccuum line also check all lines all the way back down the pass. Side of the vehicle to the evap canister on the pass side front of bed mounted to the outside of the frame rail check for cracks and loose fitting hoses, the problem could also be the valves at the front pass side of the eng. comp. a haynes man. And a vaccuum gauge will instruct you how to troubleshoot