If you pop the cover off the diff you will find the ratio or the teeth count stamped on the ring/crown gear.
The tag is not always going to be right, if the gears were changed sometime over its 20 year life they could have changed the ratio. Thats what happened with mine, somewhere down the road it was switched to 4.11s and the tag was still on it saying 3.55s!
When I was looking for an axle a couple years ago I found by marking the drive shaft and spinning one wheel to turn the drive shaft one revolution the wheel would just about make two turn was 4:10 and 3:55 would go 1 and a half to a little more. This is by tring to remeber from a while back . May be some would like to check their truck
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