take it back and have them check the coil packs. They found that mine was miss firing in 2 cylinders, causing the buck and hesitation. Another member had the same thing, and his seems to be fine now. Mine was the same in which it would stutter, and then not, very random, but the dealer has narrowed it down to this. They even had a Mazda rep come to look at it, as they couldn't locate the problem, but felt it when they drove it. I will know if it works on mine next week, I have the parts coming this week. They are also going to out new spark plugs in as well. Fingers still crossed this is it!