Gears Vs Converter

The best choice is a matched package, regardless of whatever that is. When in doubt, you can run any gear with a stock convertor and not lose any performance. You will sacrifice something by running a higher stall convertor with too high (numerically lower) gear. It may be throttle response, or gas milage, but one way or another you will lose something for what it gains you. So if you think it needs gear, stick the 3.91s in. See where it cruises most at. See how the enigne responds. See how you like it. You can pick a convertor better after you know things like typical cruise rpm and your own driving habits with that lower gearing.