There is no reason what so ever to use anything higher than 87 octane unless you're engine is pinging, and there is never a reason to go higher than 89. You don't get better performance with higher octane. Octane is basically just a measure of the speed at which it burns which goes hand-in-hand with detonation. Higher octane gas burns a little slower.
The only things I would do to improve towing are install either helper springs or helper air bags, and/or a load distribution hitch.
A lot of people on this site like the 2 degree timing advance. I haven't heard or read of any disadvantages to that, although I assume the timing set as it is gives you more mpg.
I'm not a fan of cold air intakes because of the filter you have to run. The gauze/mesh filters flow better, but they also let in more dirt unless they are sufficiently oiled...then they don't flow as well. Also, the horsepower increase with a cold air intake is typically around 2-5 hp in the 5500 rpm range, and they are noisy.
The power gain with cold air intake and free'er flowing exhaust is greater, but again, the gain is in the 5500 rpm range.