Hard starting after fuel fill

Most common reason for this is a sticking EVAP purge solenoid. What happens is that the solenoid is supposed to stay closed until the system decides to open it and draw off the fuel vapors from the EVAP canister so they can be burned through the engine. However, if it sticks open the fuel vapors as you fill the fuel tank get pushed into the engine and flood it with extra fuel so it cannot start until the fuel mix leans out enough to burn. Repair isn't too difficult and requires minimal tools, you remove the trim cover over the engine if it has one. Next locate the purge solenoid, there are two designs, one bolts into the intake and has a stem with an o-ring on it the other uses a solenoid mounted on a bracket. In both cases you remove the electrical connector, then the mounting bolt and swap out the part. The only item to watch out for is the plastic lock on the quick connect, they get brittle.

It isn't a difficult task, the bolt is usually a 9 or 10 mm. Check which one your engine has as GM changed them mid production. Until you get it done you can use another trick if you fill up, if it cranks a few times before starting, hold the gas pedal to the floor, that triggers a clear flood mode and shuts the injectors off until the engine actually tries to start and the RPMs jump up from that, then it turns them back on.
Let us know what you find, but it's a very common failure.

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