Boondockonly probably said it correctly, you have the center gasket doubled. this won't allow the filter to engage the threads without a lot of upward force. Also the tip about using only the AC Delco filters is a good one, If you read on any of the Duramax forums, this is what they tell you, unless you switch to the Cat filter w/adapter, which is just as good but a lot cheaper to change.
03 Silverado cclb 3500 drw, D/A, Reese 22k hitch
07 Alfa SeeYa Gold 30RL,2 slides,power everything