It's difficult to gauge from your question exactly where do you feel the vibration the most. For example, is it on the gearshift or generally the car or on the seat.If it is the gearshift, it is not an uncommon thing. Honda is known to make high rpm (revolutions per minute) engines which gives it the pep that you feel while accelerating. However, the downside is that these engines tend to transmit the vibration a lot more than low rpm engines.From what you have described, I sense this might be the case since you mentioned that it begins to lessen after 55 mph and is gone by the time you hit 60-65 mph. Very simply the engine rpm drops as you come to the crusing speed.In case you feel it on the seat, then it is definitely something you need to make a noise with the dealer or directly with the company guys. In all likelihood, you are dealing with either tire or transmission related problem which is causing the vibration to be felt while seated.