Chris_1

iTrader: (1)

Look up adjusting the PSOM 1993 F150 on Google.
PSOM stands for PROGRAMMABLE speedometer odometer module.
Basically press and hold the reset button and turn the key on will show you what it's set at - figure out what it should be set at for your tire size and when you're ready to actually change it you hook a wire to ground from the spot under your glove box.

hawkfall

Download a free GPS application on your phone that will list your speed, and compare it with your speedometer. If it is off by a lot then you know what the issue is...

224282

If you look on the diff lid, should be a tag. Might have a number that begins with 331 or 355. You can also look on the door jam sticker where it says "axle" and it may say something like 17, 18, 19.

andretti05

Yes, I agree with the posts so far. Changing your tire size messes everything up! Your top gear for cruising speed on the highway is meant for a certain ratio of wheel turns to engine turns. When you change your tire size, you change the power going to the wheels in different gears. By adding bigger tires, your wheels turn less times per turn of the engine than they did before, which would make you have less acceleration in each gear. Get new gears for your axles, or get tires that are the right size, and your problem should be fixed. Here's a good chart:

http://www.therangerstation.com/tech...irechart.shtml

BAMAGRAD1995

Calibrate your speedometer using the instructions in my friend's video!