I believe that if a truck has open differentals it acutally is a 2-wheel drive......
We threw one of those Eaton electronic lockers in my dad's suburban and it really works great, but you have to unlock it if you are on dry pavement or the pressure on the asles is something fierce when it turns. His truck is only a 2-wheel drive, and even with that he still buried it up to the subframe behind my barn last year. Luckily my neighbor came over with his Dodge Cummins and popped it out pretty quick.
