It's a 4.0L OHV, and probably not going to gain much on a dyno versus a canned tune from someone who has worked with rangers/explorer a lot. Now if you had an aftermarket intake, headers, bigger fuel pump, cam, those kind of things I would say go to a dyno for sure. But you could ask how much he would charge I guess if you want to be disappointed when you see numbers on the dyno, lol. It would be cool to get a real world before/after number.
If you buy tunes, try James Henson at Henson Performance
He tunes all kind of stuff, and did he an awesome job with the sport trac. Fairly quick too.