I got both heads reconditioned, put back together, notice when I drive from a gentle take off it does a putt putt notion that you can only feel when you pay attention to it. It doesn't really hestitate more so a putt putt. It happens when I drive and when I give it gas to make it down shift. I've only driven the car with the heads on here a little over 500 miles. Are they just breaking in or is it something I get looked at???