Hummer H2 CEL with misfire codes

[2007HummerH2]

On the way to work this morning, my CEL came on and started to blink. Hit the Onstar button and they said I had a misfire on two cylinders. Got to a local store and checked under the hood.....ddn't find anything out of the ordinary. Started the truck up and the light was out. Started up the road and the CEL came back on but was solid this time. I only had 4 miles to get to my shop. Called local repair fellow that is 1/2 mile away and brought it to him.....It wasn't running very well.....very rough and then would smooth out. CEL was blinking again. Mechanic thought it either had to do with fuel or electrical system (coils).
Truck has been running great till this point. Only 53K on the odometer. Not really sure what it could be.
Should I start with the easy things first....plugs, wires, etc?

 

[Scarsman]

I would lean towards plugs/wires/coils first. I wouldn't think fuel would have anything to do with a misfire.

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[Kyle]

I would lean towards plugs/wires/coils first. I wouldn't think fuel would have anything to do with a misfire.

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+1.

 

[Zach]

What were the codes?

 

[cgalpha08]

I know when my parents had one it was the the ignition coil on cylinder 7

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[2007HummerH2]

Just got the 2 back. Brought it to a small owner/operator garage. The guy is very thorough. It ended up being a P0300 and cylinder #5 coil shorting out. He also changed the plugs/wires. The factory plugs were gaped wrong so that didn't help. New plugs installed and gaped correctly. Purrs like a kitten now. Gas mileage has gone up too.....averaging 14-16mpg constantly now....before it was only 12.5 on a good day. Also for the past so many months my temp gauge had been kinda wacky, it would work sometimes and not others.....thought it was a bad gauge like a lot of the 2's have. The truck also pulled a code for a faulty thermostat. He didn't want to put a new thermostat in it until I ran it for a few days to see if everything was ok. Low and behold the temp gauge works just fine now.....come to find out it all had to do with the misfire that showed up the other morning. Evidently it makes the computer think the truck is running hot and keeps the thermostat open, which in turn makes the truck run rich. So if any of you out there have a fluky temp gauge you might want to check for codes before you end up with a blinking CEL light!

I don't have the exact codes in front of me, but I will post them up soon. I have them with the repair order.....

 

[2007HummerH2]

Here are the codes I was throwing:
#P0128 Coolant Thermostat
#P0300 Misfire
#P0335 Ignition Coil E Primary Circuit Problem
#P044 Evap Vent Control-replaced bad gas cap that came from previous owner