My 2007 Avalanche has a gasket along the bottom and sides of the cargo box that seals with inside of the tailgate when it is up (or raised, or closed, or latched, or whatever term you may use). The gasket very easily detaches from the edge of the cargo box along the bottom. I have to push it back into place almost every time I use the tailgate. If you have encountered this problem and found a way to repair it that worked well please post what you did to fix it.