I have a 07 ltz 4wd with 20000 miles on it and for the last couple thousand miles when i start the car it sputters, and yesterday it sputtered out completly twice, and had to be recranked.the sputtering/not staying startedonly seems to occure when the engine is completly cold. Has anyone else experienced a similar problem, and maybe has any suggestions on what to say the the service dept, due to the fact that it only happens during cold cranks it is goin to be hard for them to duplicate.