Starting about 3 months ago my '04 CTS 3.6 (@ 108k miles) started running a little rough. Several days later I filled up the tank, and it wouldn't start until I pumped the gas pedal a few times and held the RPMs to about 2k - but as soon as I released the pedal she dies. This happens several consecutive times - then on about the 3rd-4th attempt she starts.
After starting - she will idle rough for about 50 miles, then smooth out and starts every time with no issues.
As soon as I fill up again - same issues: Won't start, runs rough, smooths out after 50 miles or so.
Have had it to the dealer now 6 times - they have replaced gas cap, some return relay and canister in/near the gas tank (required dropping the rear end), all plugs, 2 coils, had throttle body and injectors cleaned.
Any ideas? Thanks folks!