It would be helpful if you'd include those details because that sheds new light on the issue. I was under the impression this was something new that you noticed was different from before. You may be feeling the normal vibration of a six-cylinder engine. The engine rocks to one side a little when it's in "drive", and the other side when it's in "reverse". That rocking will change how the engine sits on the rubber engine mounts, and moving like that can increase or decrease the severity of how normal engine vibrations are passed through the mounts and into the passenger compartment. The clue that this might be normal is the vibration will change when you increase engine speed very slightly.
If there really is a misfire, the Engine Computer will detect it, set a diagnostic fault code indicating which cylinder is responsible, and turn on the Check Engine light to tell you. What you might consider is visiting the dealer, and have someone from the service department sit in the vehicle and tell you if what you're feeling is normal or not. Most reputable new and used-car dealers give a 30-day 50 / 50 warranty to cover things like this. Often they won't make you pay your half of the repair bill within the first three days, but that varies by dealer. Either way, at least if there is a problem or it gets worse, you will have proof it was there right away if you don't wait to take it back. I know at Chrysler dealerships they will cover a repair long after the warranty has expired as long as they knew about it while the vehicle was still in warranty. GM doesn't have the same customer-friendly business practices, but most used-car dealers are even more accommodating.
Tuesday, June 16th, 2015 AT 6:19 PM