The code B6 means you do in fact have a 3.73 limited slip. On a ford any number letter combination means limited slip two numbers are open diff. 2 or B generally refers to 9.75 rear axle 1 and H for 8.8. 9 for 3.55 6 for 3.73 and 5 for 4.10. My truck has a B6 code and the axle tag reads 3L73 so i know its true on mine. This info is a lil dated but to the best of my knowledge it is still accurate.
CB is correct. I just purchased an 08 Supercrew yesterday and did a lot of research before hand because I will be using the truck for towing. The last page of this doc lists the axle codes and the gear ratios.
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