I have had my 96 3500 duel wheel parked most of the winter and spring. I discovered an issue with fuel pressure when I took the rig out of the yard and began getting it ready for a trip. I've started throwing fuel from the tank if the cap is locked down. I just took a trip from Nampa to Moscow and while I got 13.2 going up and about 13.6 coming back, I have to leave the fuel cap loose or the rig pumps up pressure in the tank and causes fuel to expel from the top of the tank someplace. I worry about this only because running with a loose cap should cause a fault code to throw and yet I am not getting either a hard code or a soft temp code on either the dash or my code reader. I have had back surgery last year and I don't move very well on my back crawling under even something as tall as this 4x2. Any suggestions will be appreciated.