The TrueTrac is a great carrier, I have one in my Monte Carlo. Eaton makes fine products. Personally I'd get a Detroit Locker for your application though. Reason being is that with the way the TrueTrac works, if you ever get one rear wheel off the ground completely all the power will transfer to that wheel and you won't go anywhere. On a street car TrueTracs are awesome, but I'd go for a real locker in a truck. Especially a 4WD.
You could probably get around the free-wheeling situation by applying a little brake, but in a truck I'd just prefer not to worry about it.