First, NONE of them are for Mileage... That's up to YOU! The best fuel economy is had by driving it "like an Old Lady
". That's kinda it,,,, keep it under 2,000rpm, don't push the pedal more than 1/3 of the way down (I can't drive like that, good luck!
Otherwise you're looking at @14mpg average from your 3 1/2 Ton - 450cid - "box" pushing through the air - hehehe
As for the "chip", the programming choices are made at the time of purchase (the PO made those choices). You could find out from him what they are and who the programmer was. If not, you could remove the chip from the PCM (computer) and look for a label maybe. Chances are, by now, there are better choices you could have it loaded with now anyway. I'd actually be leery about using it at all, there have been Far more BAD programmers made than good ones today that have poor programming in them and can damage things like the transmission...