[Piotrsko]

From the instrumentation tech background: you are relying on a very loosely calibrated tach and speedo for precision measuring even if the data gathered is precise. Based on my ranger experience, your dash gauges are off.

I traditionally put the axle on stands so I can observe when the marks cross the origin point and like freebeard said do multiple runs.

Or you can pull the cover and count the ring gear teeth, but the data I have is simply: there were only 2 main options 3.73 or the 4.10 which will be about a half turn extra on the driveshaft. If like you say it's "9 oclock" then its a 3.73. If its not, but about a half turn further, then it has to be a 4.10.

Finally: being a common 8" diff there are odd gearings available aftermarket, which is why I suggested you remove the cover and count teeth if you are not the original owner.

Further research on older rangers suggests that 6 cyls got the 3.73. 4 bangers got the 4.10. My documents only cover to 2000.