I'm fighting a horrible misfire battle myself although your car is 12 years younger than mine...

Firstly, did they test to see if its random sputtering or a certain cylinder misfiring?

Does it misfire all the time or just sometimes? Any conditions make it worse?

__________________
2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k