Jimmi V.
I had the same issue - found my new (cheaply made) gas cap would not allow the vapor to vent out of the cap. Has to disassemble the dang thing and clean up plastic over castings to get the vent to work properly, in this case I hade a lot of tank presure and it was forcing fumes back tru the intermediate rubber tube and the metal fitting of the tank. Fixed that issue - still had strong fumes...
Found that the rubber grommet that insulates the filler tube from the truck was again made poorly and there is a bit of a gap around the filler neck, so now when the cap vents ... go to love this... the fumes are directed directly at the gap and fill the cab real nice.
Well - only fix is to find someone who has a decent filler neck grommet - in the mean time I filled the gap from the backside with some clear silicone - stops the fumes and is not so visable.
