2001 vibration 45mph+ when on accelaration

Just picked up a 2001 sebring w/ 2.7 engine (I know!:banghead: ). Vibration is bad as you approach 45-50mph and you are not 'coasting'. Tires balanced, smooth as could be expected during coasting. Is this a precurser to the 2.7 sludge problem? CV joint? Thanks.