XC70 hesitation-runs rough
 

I own a 2008 XC70 with the 3.2 engine and has about 60K miles. After buying it about a month ago it wouldn't start and the dealer replaced the fuel pump. Afterward it was fine. But now it runs a bit rough and is esp noticeable when accelerating and cruising at high speeds. It almost feels like a tire is out of balance, but they are brand new and just mounted and balanced. When the engine is cold and I get on it first thing in the morning it can really hesitate. One time it almost stalled. Any ideas what it might be? it's in the shop for the 2nd time. The first time they found no codes. Frustrating...