Two ways:
1. Look on your driver's side door jamb--under "axle" you should have a code like "H9N" which would tell you that the factory stuffed a 3.55 Traction-Loc under there, and/or:

2. Jack up the rear end so both tires are off the ground. Rotate one wheel by hand--if the opposite wheel turns the same amount, you, sir, have a traction aiding device of some sort.

FWIW, if you're interested in Ford's breakaway spec, it is 50 ft./lbs. To check, raise one wheel off the ground, set your torque wrench at 50 ft./lbs., and turn the raised wheel by one of the lug nuts. Ford sez to do this with a special tool which poitions a turning hex directly concentric with the axle center, but...

Eddie