Issues with Mazda 6 V6 2006 Surging Issues

I'm a new owner of an used Mazda 6 v6 3.0 automatic. It was bought at a dealership when they were having an as is auction for $1000. It is in great condition other than it surges when the car is in gear, never in park nor in neutral. It will surge/ buck when it is idling or when you are accelerating but never in park or neutral. It does have an engine code that says it's miss firing, so I got sparkplugs for a tune up and was then going to see if it continues before buying the coil packs for each. But I have feeling it is more than just sparkplugsabd coils. When you put it in gear and listen to it it kind of makes a crank/ grind but not to loud. But it's in tune with the surge. The rpms never go low, and it doesn't act like it wants to stall. So wanting others opinions. Thank you in advance.