Problems opening the gas cap for removal when gassing up my 2004 Buick Rendezvous. Just bought a new cap and same problem, won't open

If the cap is hard to remove, this is a common problem with older GMs. The mating surface at the end of the filler tube becomes slightly corroded and is sticking to the rubber seal on the cap. Plug the filler tube with a rag (to avoid any explosive hazard), clean the mating surface with lacquer thinner, gently buff it with crocus cloth and try that. If it still sticks, lubricate the cap rubber seal with a thin coat of a lubricant (ONLY one approved for rubber/plastic materials).

Have the codes read.. EVAP system. Two things I can think of. EVAP, vent solenoid stuck shut or the fill tube is bent. Bent tube would be hard to insert and release.