Up through the '97 model year, you can recalibrate your speedometer by replacing the vehicle speed sensor (VSS) gear. If you have a 2WD, then your VSS is in the tailshaft of your transmission. If you have a 4WD, then it is in the transfer case. In either case, it is just in front of where the rear driveshaft enters. The VSS is held on by one bolt and has a two-wire connector plugged in to it. Mine is a blue, aluminum looking color but that may not be the case for all. Remove the VSS and at the end is the gear you need to replace. You dont' say at what speed you are off by 3-5 MPH, but you probably only need to go up by one tooth. Count the teeth on your current gear, and then get an identical one with one more tooth. For each change in one tooth, you will change your speedometer/odometer by approximately 5%. If you put a larger gear in, your speed will go down, a smaller gear will make your speed read higher. The last gear I bougt in March ran about $10 at Ford.
The part number I needed for my '97 5-speed auto that originally came with
4.10 axle and 255 70R16 tires was C0DZ-B. It is the 19 tooth pink one. My original gear was the 20 tooth black one. One less tooth was all I needed. I used this formula: New Teeth = (Current Teeth x Speedo Reading)/Actual Speed. Be aware though that the table came from a Ford Ranger site. Unfortunately I don't have the link anymore so I don't know whom to give credit. The gear I used says that it goes on a manual transmission. When the parts lady first brought out the 19 tooth gear for the automatic, it was too big. Fortunately I took the gear out and brought it with me to compare (boy did it shift funny without the gear!). Here is the table that I used:
Manual Transmissions and all 4x4s:
16 tooth wine(C0DZ-A)
17 tooth white(C3DZ-C)
18 tooth yellow(C0DD-B)
19 tooth pink(C0DZ-B)
20 tooth black(C1DZ-A)
21 tooth red(C4OZ-A)
2WD Automatic Transmissions:
16 tooth blue(D0AZ-A)
17 tooth green(C7SZ-A)
18 tooth gray(C7SZ-B)
19 tooth tan(C7VY-A)
20 tooth orange(C8SZ-B)
21 tooth purple(D0OZ-B)