[dirtyjim]

before trying to seal the grommet I would make sure the tank is lined up where the filler neck centers up on the hole in the cab. there is a little adjustment on the tank.
what is the condition of the grommet? if its new and the tank is lined up I don't see how gas would get past it, at least on my truck.

when I first bought my truck I had the same problem, a new filler neck grommet and aligning the tank stopped it