First off, be glad that it's starting to warm up a bit! I fought this on my car (06 LT) for I don't know how long, and the missing plus the cold (lower 20s and colder) made her stall out on me when coming to a stop! :(
Try checking/changing the spark plugs. Yes, it would probably be covered under your warranty, but for the price of them, esp. w/out a CEL, it might be something you just want to go ahead and do yourself. And you'll thank yourself if it fixes it.
If it doesn't fix it, good luck. I ended up having to replace 2 of the injectors (had my mech. do all 4 while he was in there, though) before mine would stop missing. Well, not stop missing, but drastically reduce the amounts (mine was missing enough to throw the CEL). There's still something going on, because I can feel her missing, but the $300 I spent on having my mech. replace the injectors has GREATLY reduced the vibrations I feel in my butt!