why is my tighten gas cap display keep going off?

agree with #1

Possible EVAP system problem.. Need scan test from a repair shop.. Not parts store! .. Service engine soon light on?

You may need to go into the on board computer to clear a trouble code. Also, did you install a GM cap or purchase one from an auto parts store? I would recommend and OE cap.

I had that problem with my 04. I changed the vent solenoid and it still came on. I found out that there is a new type of solenoid with a vent lead that goes to the top of the tranny that fixes the gas cap issue. It says gross evap leak code.