check engine light keeps coming on -code saying large EVAP leak but cant find it

Hello, This is straight to the point. There is a pressure sensor in the fuel tank that is alerting you that pressure is not building up. The pressure sensor may be bad, or there may be a leak. If pressure testing and smoke detection do not work, there is likely not a leak, and the sensor should be tested. If you need help diagnosing the vehicle, send me your questions, but if you prefer to have the vehicle professionally diagnosed, here is a list of certified service centers in your area: http://repairpal.com/chevrolet-within-10-miles-of-east-syracuse-new-york-13057