I bought an xcal 2 last year for my sport trac (4.0L auto), and it was a nice change in performance. I didn't notice it as much when I started using it, and ran 92 octane all the time. But when I switched it back to stock after a couple weeks on 87 octane (for curiousity), it felt like such a dog!
You won't get much benefit running an 87 octane tune, but the shifting will make a good difference. The main power increase comes from higher octane fuel.
A good tuner will firm the shifts up, raise shift points, and give a bit more power.
I bought mine from James Henson at http://www.hensonperformance.com/
Since I bought the F150, I had him write tunes for it also
A tuner (imo) is the best bang for the buck, especially with an automatic (remember they are computer controlled and they can change anything with software).
Plus with an xcalibrator, you can change (on your own) gear ratios, tire size, spark, change some shifting stuff, change/remove speed/rev limiters, etc.
There are a few things that would change the way he would tune yours, like headers or aftermarket intakes. A catback exhaust normally doesn't change anything.
A new/updated tune from James (if you change something on the truck) is only $50, and he is pretty quick to write them.