Mine was doing the same thing and it turned out to be bad O2 sensors. I want to say it had something to do with my downpipe but I have since taken that off and changed out the bottom sensor and it has been fine since then. Hopefully that helps. Good luck

 

have a 3in catless and trifecta tune, had Vince delete the o2 sensor when I got tuned so iwouldntpop a CEL.. Could it still effect the car?

 

Funny you brought that up because I started to think about my stock downpipe on my way home from work today, figured that given the symptoms, it would be make a bit more sense if it was coming from there. I had a Cat go bad on my SS SC, it felt odd for a bit but still performed then one day it just popped and a CEL came on along with a rattle from the Cat. Hopefully something will trip soon, thanks again for all the help guys, i'll be sure to follow up on it.

 

I had my car in last wednesday to get my yearly inspection done and to mount a set of tires. They had to turn my brakes and change the pads but they couldn't finish it all in 2 days and I needed the car for work the next day...................no idea what they were doing for 2 days other than putting greasy fingerprints all over it and spilling oil on the engine and charge piping but anyways. I'm taking it back again Tuesday so they can finish the brakes and take a look at the shuddering.
I noticed the other day as I was driving home and it was acting up, the Air/Fuel ratio would go anywheres from 9.5 to 18 (as per RPD) but mostly from 10 to 17 and anywheres in between when it was taking one of its spurts. While it's doing this, the fuel pressure is staying steady but you can hear the BPV releasing air it seems. Eventually it'll snap out of it and start driving half normal but still slight hesistating before the next time it goes nuts. WOT it still runs pretty good but not as good as it should be.
I took a video of my Air/Fuel gauge going nuts so the smart people at that GM dealership do not call me and tell me that there's nothing wrong again. I really do love this car but trying to get it fixed it such an ordeal, it seems like the Techs around here are lost without a CEL, not too mention how my car has been treated while in their custody (ie: Greasy fingerprints all over it, oil on the engine/charepiping, damage on the bumper etc...) and of course, needing more than 2 days to do an oil change, tires mount, and brakes. DO IT ALL AT THE SAME TIME IDIOTS!
As much as I do not want to say this but this will be my last GM because they just don't care, they have kids working there that wouldn't even cut it at Canadian Tire and they're using my car as a training prop even though I am constantly yelling and fighting with them about it. This is my 2nd GM dealership.

 

Time for a new dealership man, no way should your car come back with oil on the seats or spilled in the engine bay. Dealership I used to take mine to put a plastic bag over the entire seat so they couldn't get prints on it.With the symptoms the car is either not getting enough fuel, not enough air or no spark under partial load. Dealerships suck at diaging things that don't set off the CEL or that don't happen unless your moving because they don't do real time logging that I know of. If you lived closer I'd say bring it by but well....you're a hell of a long way away