My opinion may not be welcome here, as I love OLD SCHOOL stuff.
If what you're after is a lightweight rocket, why not just hop-up a Honda Civic? If it was my truck, I'd put some vintage speed equipment on the 261, let that sweet 6-cylinder rap fill my ears, and grin from ear to ear, even while being passed by every import on the road.
Heck, my wife drives an old (2001) Chrysler 300M that almost meets your criteria, and gets 28mpg highway.
But, it's all about what you want to do. As 4t6 says, have fun and enjoy it, whatever you decide to do.
I LOVE the AD truck styling and its build philosophy (simple, exposed metal in cab, only 4 soft surfaces in cab, easy to see how everything on it works, etc). The ONLY critical things I really want to CHANGE are to add a bit more power, and air conditioning (so I can use it daily - I live in Texas). The other mods are just to get the icing on the cake: having a pickup truck that weighs under 3000 pounds is just plain cool, in a world where trucks now START at over 4500 pounds, and go well past 6000 pounds. It satisfies the engineer within me.

Jim G