Oh, forgot to mention, is that the factory cat on there? Tend to plug up & rob power that will progressively get weaker as time goes on. If there is a rattle on cold morning start ups time for a new cat. No rattle, crawl under, give the cat a hit with handle of a screwdriver or hammer & if it sounds like a metal box of marbles, thats a big part of his power loss.
Besides what I listed above, some headers, ypipe & h/f cat will help it tow like a champ plus give it a much better exhaust note. Biggest exh restriction is right infront of the cat. 2 small dia. pipes bend sharply right before going into the cat. Put in slightly larger ypipe & straighten out the entrance into a h/f cat can give noticeable gains & much improved note even without the hdrs.
If he has deep pockets, could do what I did & the others suggest