I have access to machine my own TB's and I have mine Ported out to 73mm on my Dodge Charger. MPG dropped a little, but not much. Throttle response was improved and it pulled a little harder in all the gears. I went through 3-4 cuts and Flow tested them before we found the best cut.
Hypertech makes a Tuner for the 3.5L, but it's only a 9hp Gain. If combined with CAI, Ported TB and Exhaust. Would be the best set up.