yea, just a tune-up would do a bit. it would get the truck running to at least what it should be. powerwire...i'm not to keen about. i mean, maybe if you drive very lightfooted, like u said u do, maybe you'll get better gas mileage...but it my case, it eats away at gas mileage...
and like mag said, maybe a free flowing muffler would help, but again, i mean u spend $300 on an exhaust to HOPEFULLY get .5mpg more...it seems like it would take too long to pay for itself at .5mpg.
also, try different gases. our trucks are supposed to run on 87 the book says, but try 89, see if it's worth the price increase for the mileage increase. throw some of that fuel system treatment in your next fill up to. in my maxima, i throw one in every tank along with 91+ octane...(it gets filled like once a month...cause i never drive it in summer). and that $3 bottle of gas treatment adds 60miles to the tank. at 17mpg, that's like just about $15 in fuel savings in a $3 investment.
what kind of wheels do u have? the 17's, or do u have some heavy ole' twenties? centerline has wheels are that lighter than hell...that'll save on gas.