how could i find out what rear end gear is in my truck?i bought it used..2003 supercrew xlt fx4

 

Code is on driver side door post. Match it in your manual

 

I think all 2003 Supercrews with FX4 17" wheels have 3.73 rear ends, but the axle code is on the sticker on your driver's door.

19 = 3.55 open
H9 = 3.55 LSD
26 = 3.73 open
B6 = 3.73 LSD
27 = 3.31 open
18 = 3.08 open
25 = 4.10 open
B5 = 4.10 LSD