what are the best mods for my '97 expedition (5.4L) for towing? exhaust (cat back, headers, complete system, manufacturer), chips, intake?

 

I have a 97 EB with only the K&N filter system and a good tranny cooler and mine tows a 18foot pontoon all the time with no problem and before moving west for a few years I was in the Northeast with a lot of hills. I have had friends who put on the cat back and actually lost towing power but it sounded good.