Not to be cynical, but, it seems that many of you just bought whatever Expy that was on the lot without first looking at what you were buying !!!!
Even buying used, you should be able to figure what packages are on the truck.
When all else fails, read the manual. When it gets to a specific point, look at your truck to see if it has that particular piece of equipment, i.e. if the manual shows a picture of a "locker button" and your Expy has that button....you have a locker.
Then, again, if all else fails, use your "MK 2 Eyeball" to see if your rear axle has the necessary lines for a locker...
And if that fails....look at the door sticker as mentioned in a previous post....for the axle code....that will tell you what axle you have.....
This is not rocket science !!!