Great.... nothing is ever easy
The 3.31 gear is Motive and the 3.27 or 3.55 is FMS.
Ford does not make a 3.31 damn it decision decision.
I was prefering 3.31.
I did you the calc for tire size which is 25 in.
Here is the breakdown at 60 mph
Keep in mind I am currently at 3000 rpm @ 60 mph = 3.73
1. 2500 rpm @ 60mph = 3.08
2. 2650 rpm @ 60mph = 3.27
3. 2700 rpm @ 60 mph = 3.31
4. 2900 rpm @ 60 mph = 3.55