Why the car keeps misfiring!

I have a 2009 Traverse that has been plagued with misfire problems, check engine light on constantly. This car would misfire under load-especially with the cruise control on, going up a gradual incline or hill. Dealer I ordered the car from went through lots of pain to get it cleared, a credit to them, but they never fixed it- just kept trying until warranty was up. They replaced every coil pack with Bosch copper coil packs (original 3.6 comes with aluminum in 2009), replaced all three catalytic converters, starter, flashed the computer and did every recode available including the one that is supposed to fix misfires. After warranty was up, I did my own work as I am a step up from a shade tree mechanic. I took the car to my local Firestone dealer and had them check the alternator. They said it was a bit weak but should not cause misfires, but I should consider replacing spark plugs. I know plugs don't go out much, but I figured why not so I bought some high-dollar plugs with multiple ground heads so I get plenty of spark, right? I went to put in the new plugs and found one was only finger tight from the factory. Dealer never replaced or even inspected them!! So that worked for about a month and then check engine light came back on due to multiple random misfires P0300 code. Great! Ok so I suspect an air/fuel ratio problem and changed the mass air flow sensor and all 4 O2 sensors. I also checked the entire exhaust for leaks since that can cause it too. Still misfires!!!! So I read up on the Acadia forum about this misfire problem and they say spark plugs are to blame. You must use OEM AC Delco plugs or the computer goes stupid and doesn't know what to do. Today I changed out the high-dollar spark plugs for the AC Delco 41-990 plugs. Took it out and have no more misfires!! Ugh! After all that and it was spark plugs?!?!?! So I am passing this on to all of you so you don't have to go through the mess I have to get back on the road!! Happy motoring!!

sounds like you may have a problem with the variable timing solenoid for the cam. Or the exhaust cam phaser.

Sorry, didn't see date of post. this site organizes comments poorly

I'd suggest first with this issue check compression then plugs and coils. I have seen these 3.6 engines burn valves . Gm should recall the whole motor everything about em from 09-14 suck