OBD Code 0442 Means ...
 

2004 Silverado 5.3 V8.

... that your gas cap is not fully screwed down. Ha. Had a check engine warning light come on and read the code after I got home. "Evap System Leak (small)." Called my mechanic and he said it was likely the gas cap. I screwed it on tight and will see if the warning light comes on again. Almost a nuisance message. Maybe it has deeper meanings like the gas tank has to be sealed or something else will happen, more serious. I drove for almost one hour to get back home with the warning light and the truck ran fine. So, no big deal this time.

Re: OBD Code 0442 Means ...
 

0442 means the tank pressure either bled off too fast or showed vacuum or pressure and didn't change when the PCM ran an EVAP test.

I believe you have to erase the code once it lights the money lamp.

Loading the parts cannon is the expensive way to fix it.

The gas cap could be the problem or maybe not. Mine turned out to be the tank pressure sensor.
I went through the troubleshooting steps in my build thread.