Front axle?

To chane to full lock or LSD.
The differential would need to be changed. There are several different typs;
Full Lock or, "Spool". This is most agressive but for off road only as it will tear tires apart on road.

Limited slip differential, (LSD) allows some movement between the 2 wheels and some have adjustmetns to lock tighter or loosen up depending on what conditions the truck will be in. It is easiest on tires the softer or more mothon is allowed between the wheels, nut knock as much grip. A stiffer setting or less wheel difference in speed is more aggresive, but it perfomrs near a spool and a lot of off roaders don't use spools as they are tough on other internal parts. It will be easier on tires as well.

There are a ton of different designs based on the limited slip idea. One company called, "WAVETRACT" has a differtial that puts power to outer wheel instead of inner which keeps the rear end from kicking out.

Detroit lock use a ratchet type mechanisme to allow wheels to go different speeds. However they are loud and tough on tires.

It is not cheap to get an LSD that is the best mix for street and off road.
I found an example on the web, look into Summit Racing as they have good prices. They take 4-10 hours to install. So labor costs depend on where you take it.

Below is the URL;

http://www.drivetrain.com/parts_catalog/positraction/noslip_toyota.html

No problem, I hope it turned out well for you.