2006 Pontiac Solstice Sputter In Engine

I have a 2006 Solstice that just turned 13,000 miles and 3 months out of warranty. About a month ago, it developed what I could best describe as a sputter in the engine, most notable in 2nd and 3rd gear with a slight load on the engine. Hasn't gotten worse, but it's an annoyance. Took it to the dealership last week and they ran diagnostics on it. Other than a couple of "loose gas cap" warnings, everything checked out ok. The did do a flash update to the computer. However, problem still exists. Took it back to the dealership yesterday, they had the car all day. The cleaned the fuel injectors, ran diagnostics on it again and said they can't find anything wrong with it. Which is good, but bad at the same time. The problem still exists. If anybody has any input, ideas, words of wisdom, it would be greatly appreciated. We love this car and take very good care of it. What in the world could be causing this "sputter". It's much worse with the air conditioner on.I have taken out the MAF and cleaned it twice with electronic cleaner. I could swear that cleaning the MAF did make a positive impact, the sputter doesn't seem as bad, but still exists. Before I fork out money for a new sensor, I was wondering about repercussions of running it for a little while with the MAF sensor unplugged to see if it ran any better. Any input is appreciated.