I have had my 04 Duramax going on three years now and still haven't resolved this issue. When the tank gets about 3/4 full when filling up with fuel the nozzle shuts off and if you look in the filler neck there is a lot of foam. Then it takes forever to fill the rest of the way up due to stopping and waiting for the foam to settle down and so on. Several friends of mine do not have this problem with their Duramax's. I have looked at the filler neck from underneath of the truck several of times and there is not a kink in it, is there possibly a vent someplace that could be plugged up? Thank you for the help in advance!