Probably not motor mounts at only 55,000 miles. Belt tensioner shock and spring could be worn, but I wouldn't think so at such low mileage. Maybe an injector issue such as imbalance or wear.

__________________
2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900