I've searched all I can, now I have to ask for help.
This is my second post here so I'll give you the run-down first.
'98 f-150 4.2 5sp 2wd. I purchased it a few months ago with 28K miles. It now has just over 31k on it. I replaced the stock wheels with a set of 17 inch "take offs" from a Lincoln Navagator and new tires that totaled 31.5 inches tall (I promptly fried my clutch). I also put in 4:10 gears, replacing the too tall 3:08 gears (I highly recomend this for more pulling power). Now my speedometer is all out of wack and I am racking up way too many miles. I have been looking for a chip or whatever to fix it. I am using it as a work truck and I am very happy with it. Any ideas?

 

Welcome to FTE! Glad to have you here.

I do believe the dealer can reflash the computer to correct for the overall final drive changes.
Call the local Ford dealer service dept and ask them.

Also, I'd guess a speed shop with a handheld tuner could do the same thing.

Glad to hear you like your truck. How'd you find a '98 with only 28,000 miles !?

 

I was looking online for a work truck, and I found a local guy who used this to tow his pop-up camper. He bought his wife a new suv (Jeep I think) with a v-8 and the truck became obsolete to them.