failed the nox section of the emissions test

Hello,
My 2000 chevy blazer failed the nox section of the Colorado emissions test. The first time, I thought it was due to the car sitting for a long time. I put in one bottle of seafoam and drove it then took it for testing. After the second failure I had a guy replace the spark plugs and a vaccum hose. Well to no avail as it failed again. The check engine light was on so we investigated and found the unplugged wire to the fuel vapor pressure sensor. Well, after getting that fixed I thought maybe it will pass now. Well it didnt. Considering this vehicle sat for a long period last year and had the transmission repaired in Texas.......now in Colorado, will this effect the emissions nox? We had a mechanic come and say that the computer needed to be flashed but everything else seemed ok. That was before the last retest. He said that the Texas gas is different and that the car hasnt caught up??? Consider, I have drove this car since April in Colorado. What should I do next? I am trying to find a job and this no car situation is killing me. Thanks