On my 2001 Ranger, I have noticed that the speedometer is of +/- 10mph all the time, I confirmed with two different ODBII readers.
Is the instrument cluster bad? OR
Is the speed sensor on the transmission dead?

I really hope it is not the latter, I don't feel like dropping the transmission to fix it (no lift at home), nor feel like paying someone to do it for me.
If possible is it a re-programming issue on the ECM or TCM? If so can it be re-programmed without paying a visit to my local Ford dealer?

 

In 2001 the speed sensor is on the transmission but external so shouldn't need to drop the transmission to change it, its called the OSS sensor on 2001-2011 Rangers
Just 1 bolt and 2 wire connector

Its possible its a speedometer error, it uses a separate electric motor than the odometer, but not sure you could see a difference between speedo and odo of 10MPH
Speedo and odo share one speed signal coming from the computer

You could get a Bluetooth OBD2 reader, they are cheap and then watch Live Data, the speed, on your phone(free app) to see if the speed signal in the computer is correct and the cluster is the issue, these are also handy to have in any case
But if both match, OBD and speedo, then OSS would be the most likely issue

This is assuming its BOTH high and low, if its just low then could be tires are larger diameter than stock, so needs a computer correction using Forscan tool

 

Idk about your truck but I'd much rather change the sensor than the dash cluster. That thing is a pain to get out. The sensor is on the tail end of the transmission, near the driveshaft. Kinda looks like an O² sensor sticking out with a couple wires. Maybe a 5 min job.
are you sure the tire size is correct, though?
Do the tires match the size on your door placard?

 

Thanks for the suggestion on the BT ODBII reader, that is how I confirmed the speed difference. I think I will try replacing the OSS and see what happens.

 

Yeah, the cluster is a bit of a nightmare to do, however, if the new OSS does not work I'll look into a new cluster, I'm missing bulbs on the tachometer and the low end of the speedometer. Hope it's just the OSS, I can live without dash lights.