Trouble code P440. Just changed fuel pump assembly. Where is EVAP purge valve ? on 1997 GMC Sonoma

I purchased a CarMD system and it says it is the purge control valve. Any other ideas ? I have also replaced the gas cap. I can drive the truck several days before the check engine lite comes on. Only seems to happen when the fuel level gets close to 1/4 tank.

Asked by for the 1997 GMC Sonoma