Trac-lok is Ford's name for a limited slip differential. What you're referring to is traction control, that can be turned off with a button.
You can check if you have Trac-lok by looking for axle code E or XE, or just doing a burnout and see if both wheels spin.
Going from 3.27 to 3.73 is a proven performance mod, but you definitely will want Trac-lok if you don't already have it. Keep in mind, the Ford unit is obsolete, so used is your next best option, then rebuild the clutches. You can search Ebay for M-4204-F288, and maybe find a new old stock unit. But make sure it's for an IRS diff, there's a difference.
Also with 3.73's, expect a major hit in hwy gas mileage, like a solid 2-3 MPG drop.
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