Starting rough then better???

Started running rough then got better???

I'm new here... and I'm having a problem with my recently purchased 07 GT. I hope someone can help.

I was heading home today and after driving a couple of blocks I made a quick turn onto another street and mimmediately after that my car started running really badly. The idle was very rough and accelleration was horrible. The sound of the car changed dramatically as well, almost like it was straining. I had no warning lights and I continued to drive the car. The poor running coninued for maybe 10 or 15 miles on the freeway (chanigng speed often, rush hour on the HOV lane). A little while after I returned to surface streets it started running better. Seems to be running pretty mcuh OK now, but kinda hard to tell. It is rainning off and on, but I didn't go through any signifigant water (maybe a couple inches max, at lower speed). I did check the smart junciton box, but it was boen dry (does that apply to an 07?) Not sure really what to think or do. Makes me really nervous about ending up broke down somewhere.

Help a newbie?

It was probably around an 1/8th of a tank. Now, I've filled the car up coser to 1/4 tank since I've had it due to not really being familiar with the distances I can go. Along with that, I remembered I did take a longer trip and ended up stopping at a small run down gas station and haivng to fill up there. I noticed the car running rougher after that and assumed it was stale gas. So, I'm wondering if maybe I had a little water settled out in a low point that got stirred up? With that idea in mind, I ran the car down pretty low and put in a bottle of Heet (water remover) and filled up at a reputable station with good turnover right on the freeway. So far it's been running just fine. So I'm hoping that might be it. Of course, I'm open to any other ideas.

As far as the MAF and throttle body, the car only has 14k miles, how often should I clean the MAF? There was already a CAI and exhaust put on the car. I have no idea if the MAF is original or not, or if a tuner was used on the car or anything. That's the next thing I want to figure out.