I've repeatedly seen higher milage using shell 93 and sunoco 93 vs 87. This is true in my caddy too.
It's my *opinion* that 1/2 the reason is because of carbon build up. If I run 93 for a while then switch over to 87 I'll get the same milage for a few tanks then it'll slowly degrade. I switch back and the milage instantly jumps up.
This is not true on the caddy though. The caddy will see an instant 2mpg change within 1-2 tank fills.
As far as the ranger.. I'm now getting 21-22mpg in 50/50 driving. (fx4, 4.10s, x-cal, underdrive, e-fan, K&N kit, magnaflow aftercat, and the tires are slightly overinflated) This IMO is pretty good because I started off in the 16-17 range. And I now only have to fill it once a week because I drive about 350-370miles. Got a lot more punch to it too.