I have the Powertrax No-Slip in my front , and it works great!!! The only thing that will change , is that both wheels will have traction, because as of now all ya have is open up there, so the wheel that spins gets all the power! 4 auto is nothing more then 4 hi, except the amount of power is split as needed. This means when you engage it , it may be a 80/ 20 split. When you slip the rear tires, it goes 50/50. All the while , with a locker, both wheels will have power.
I will say this though, plan a afternoon installing any locker up there, and try like heck to get a lift, as it is near impossible to do it on jack stands. Email me , if you want a blow by blow description. The entire axel has to come off the truck, and the passenger side of the axel needs taken appart at the shift fork.
