NC_VX, what "lockers" are is a manually controlled differential lock that makes both wheels get power. On 4X4 vehicles you can lock the front, rear or both diffs. ARB makes one of the best units available for Isuzu. Very handy for serious off-roading as often the wheel with the least traction gets the power. Limited slip helps, but as the name indicates it's limited. Where limited slip really shines is on the street where it's most effective controlling wheel slip.

As Eckstream points out, you can do a great deal to improve your braking performance by upgrading the stock components.