I have a 2002 Chevy Tahoe LT with Auto Ride

Hi I have a 2002 Chevy Tahoe LT with Auto Ride. Mileage is 138,000. Recently car was running a little rough with some rough idle and hesitation, shaking when paused at lites and on entry/exit ramps. My service engine soon light came on and stayed on. Took it in for diagnosatic and got several codes saying it was mass air flow sensor and randon misfires. They tried cleaning mass air flow sensor but did not help and they replaced it saying it was broken. Also did fuel injection cleaning as I had never done it before and thought it would help. Serv enginine soon light stayed off for several days and car was running smooth again. Then light came back on. Rechecked codes and got different one saying lean mixture present. They tested my fuel pressure and it was lite at around 40 lbs. They felt fuel pump was fine so changed the fuel filter and then pressure wenrt back to 60 - 65 range. All was good fir several days and then the serv eng soon lite came back on. I kept reading about gas caps being a possible cause so I changed the original cap that was on truck with a chevy tahoe suitable match. Drove around 25 miles or so and the lite went off and thewn stayed off for a few days more. Then it came back on. Car seems to be riding and feeling very smooth. I am at wits end with all the diagnostic steps and costs. What else do you think it could be? Does this lite need to actually be reset aftera repair or does it reset itself if the conditons for codes are no longer present? I have inspection coming up for emissions and it won't pass if the lite is on. Thanks for any input. Paul