Another thought that popped in to my head - the pressure inside the tank might contribute to the gassy smell by pushing fumes or liquid through any small leaks in the filler neck, in to the cabin. But the tank's outlet and return lines will see the same pressure. So it won't affect fuel pressure, since fuel pressure is between the pump and the regulator. Doubtful that you would have over 28-36 psi of tank pressure under the cap since that would blow the tank up like a balloon. Just saying, don't get distracted by the odd things. There's a spring-loaded relief valve in the vent line that holds a small amount of pressure before venting. And a valve in the cap to let air in if pressure goes negative. So, the gas heats up, pressure builds, the gas cools down, the cap lets it reload. Also, on fuel pressure - a clogged filter could lower flow and pressure. Another simple fix, but only need to look at it if the measured pressure is low.