so my 98 k1500 has been throwing the p0440 code lately. the light will come on and stay on for a little bit and then turn off randomly. I looked up the code and it gave me multiple possible issues such as the fuel filler neck, a purge solenoid issue, a bad gas cap, or a catch canister issue. I went to get it inspected when the light was off (I've passed this way before) and i failed this time and the guy said the gas cap was good. does anyone know the common problem for this or have had this problem before and where should i start?