First things I would check in the shop are fuel pressure, cam/crank signals.

 

I tried the MAF sensor trick I disconnected it and drove around the block with it and the car ran fine, I reconnected it and the car still ran fine... Thoughts? When it was disconnected I just noticed it was sucking in more air than normal


p.s its the on located at the end of the throttle body where it connects to the intake marked abc correct?

 

Timing chain, crank sensor...sound legit to me....
(didnt know the newer models had timing chains)

 

Catalytic Converters are harmed by leaded fuel, not by high/low octane fuel.

Here's a good read if you're not sure how octane works:
Mythbusting Octane, The Truth About Gasoline

If you're running supreme still, I don't think any other troubleshooting will be reliable.

 

Every GM engine except the 3.4 DOHC, Aveo 1.6, Tracker, and a couple others use chains.

 

I just fixed an 03 monte with the 3.8L that was starting and stalling, running rich, and misfiring.
First problem was the negative cable that goes from battery to the body near the battery, it looked ok, but when I removed it, the underside was rusted and making poor contact. cleaned the body and cable end, then put it back together.
then I unplugged the MAF sensor and it ran perfect, plugged it back in and it would barely run. Replaced MAF and all is fine.
The MAF is the black approx 2"X2" sensor located in the throttle body facing up, just beyond the flexible air intake hose.

 

Finally got the fuel filter off and you could barley blow any air through it, so it seems that MIGHT have been the problem -> lack of fuel at start up... I will let you all know tomorrow, unfortuantly I came home to my tent garage collasped on my brand new paint job covered in snow and ice damages estimated at 2700 after 1500 for the paint job F.M.L