The factory option upgrade cost is in no way comparable to the actual cost of having a dealer source all of the parts, and install them. I'm just guessing, but I bet the rear locker assembly from the parts department is over $1,000 alone, never mind the controls for it, labor, switch, fluid, etc etc. And that's IF they can get it to work. What if there's a main harness somewhere that's different on e-locker trucks? Or if they can't set the option code due to something else in your vin. I'm not trying to discourage you, just saying it's a lot more involved than people think, and most dealerships aren't going to be ready with the technical expertise to pull this off, as it's outside of their normal operation. Like I said, not trying to rain on your parade, if you do want to have them do all this, start asking a LOT of questions before signing up for the bill.