I'm not sure what you mean when you say stock performance. I would go with Bill's custome tunes, 87 Performance, 91 Performance and on the towing, if you are occasionally pulling a utility trailer or a bass boat, I would go 87 but if you are towing a camper or car hauler, I would go 91.

Keep in mind that if you occsioal tow, it is much more convient to have a tow tune that matches the octane you will us emost of the time. That way, all you have to do is change the tune, without worring about getting the tank empty and filling up with a higher octane.