I have a 2012 V6 RS. For about 3 weeks now, it's had acceleration hesitations. Sometimes to the point of feeling like someone rammed you in the back but no one is there. I can be at a stop sign and after about 2 seconds of sitting still, it will have a slight bump like you were hit and no one be there. Worse time it does it it entering a ramp to get on interstate. Any ideas? I've taken it in and the shop foreman drove it with me in it for 30 mins and it never acted up.