When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
If this is for the '94 F150 you mentioned, there are a number of limited slip differentials available for that rear axle, as well as locking differentials and selectable-mode differentials too. In an F150 of that year, the rear axle is a Ford 8.8". If the truck is 4wd, the front is a Dana 44 TTB (twin traction beam).
You might want to go to one of these websites (listed below) and read about what differentials in general do and how they work, then read about the different choices of aftermarket traction differentials available and how each one works, to better make an informed choice about what kind may be best for your intended use.
GasMonkey, the front/rear differential choice is going to be pretty easy for your situation- since your F150 is 2wd, you can only put one in the back axle. The front axle doesn't have a differential at all, as there's no power going through it, it just holds up that end of the truck.
Traction differential prices range from about $300 to $1000. Most are in the $300 to $600 range. The selectable lockers (E-Locker, Electrac, ARB, etc) are the most expensive and the easy-install caseless auto-lockers (EZ Locker, Lock Right) are the least expensive. Most of the limited slips are priced in the middle ground (Eaton Posi, Trac Lok, Auburn, etc).
Rezvani's Latest Post-Apocalytic Monster Is a Ford F-150 Raptor Underneath
Slideshow: Called the Fortress, the 850-horsepower pickup combines Raptor underpinnings with military-inspired features, survival equipment, and a starting price of $285,000.