Here's a question. How can I tell? Is there a way without crawling under and reading the numbers off the diff?
I know that I am getting the LSD in my 01. But how can I tell which ratio?

 

Look at the tag under the hood near the grille or in the glovebox. A small white tag will give you the info. Hope this helps you out, cumminsboy

P.S.- somebody correct me if i'm wrong please.

 

jack up the rear diff, put the tranny in neutral.

spin a tire slowly. if the pinion rotates just over 4 times for one revolution, you've got 4.10's. if it's about 3 and a half times, guess what ya got?

 

What happens if both tire spin?

 

Well.. with LSD one will spin faster than the other right? Or perhaps with LSD, you will see the wheels morph into this psycedellic melange....

 

 

So, that's what that was!!!

 

If you have stock sized tires......
2000 RPM = ~ 62 MPH with 4:10 gear
2000 RPM = ~ 68-70 MPH with 3:55 gear.

 

my tag under the hood says i have a 3.5 ratio but at 62mph im running 2000rpm. go figure

 

halerazor- Shovelheads numbers are good for automatics

 

so do all manuals have a 3.5 ratio, i've heard guys say that their manuals came with 4.10's. I can't imagine having 4.10 gears, I top out at 80-85mph right now with 3.5

 

You can also talk to a service manager at a dealer and he can type your trucks serial number into his comp and print you out a list of all that the truck originally came with, it will also tell you what type or axles you have as well as the gear ratio.

~~~
IRT Shovelhead: my 1999 quad cab shortbed 4x4 automatic ran at 1900 x 60 mph with stock tires and I'm running 4:10's

 

I was running at somewhere around 1700 at 65-70.