Grab a 4wheeler magazine off the rack and check ARB as Howard said or the dozens of other MFG. out there.
I like limited slip in front and rear. THe older ford's were great because you could adjust the clutches for your own liking.
I set up the rear to be almost a full lock and the front to slip on the corners. True detroit lockers look like a ramp with a wall at the end. Going forward it's wall to wall but going around corners they can move backward to allow a little slip. This also happens when you back up.
Spool locks are full lock up with no slip. most ARB's are this type. There are lot's of options out there.
I have a 2003 F350 SD Crewcab short box. I had limited slip in my old truck and it was worthless. I was looking at True Trax. They have units that just replace the spider gears in the carrier, so you don't have to remove the carrier. That way there is no setting up backlash etc. One other company makes units that use a planetary gear set up, so the can be used in the front. How long have you had the ARB. Are they reliable?
i had an 84 chevy k-20 that i used for plowing that i also used for 4 wheeling. i put a powertrax in the front, i liked the additional traction but it put a lot of strain on the front end when turning, also a lot of jerking. its real noisy when turning. i think an air locker would be better when you need the additional traction, but disengage it when you dont.