I recently had to hunt up a replacement filler neck for the fuel tank on my 2000 K3500. While I had fuel tank out to replace rotted brake lines I checked the filler pipe that mounts to side of bed and found it badly rusted on top (looked great from bottom). Those necks are real expensive at dealer and scarce at bone yard because they seem to rot out a lot. Pull and check yours and rust treat and protect it as needed. Mine actually had many rust blisters inside filler neck where outside rust was penetrating it requiring its replacement. Another point, I am adapting a filler next off a 96 to use (it is shorter and uses a longer hose) as the 96 one I found in bone yard was galvanized and 2000 was not.