service engine light 2001 silverado 5.3

My gas started screwing up when the tank is full reading empty and low fuel light comes on. I figure a bad sending unit on top of this my service engine
light came on with the fault code p1441. The gas cap is ok in reviewing the manual it sounds like I need to check the purge valve for the evaporator system Where the dickens is it located?I cant find it. Thanks in advance
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