Back to original question.. I would wait and find a truck that has what you want. I almost bought a 15 that I was told had a limited slip (I later learned none of them do anymore).. I had papers signed and everything then dealer brought in original window sticker and I noticed it said regular axle. I squashed the whole deal right there... They said they would put the locker in it if I still wanted but after waiting for a half hour they came back and said it was much too costly to add it. I believe service quoted 3500 and said the whole rear end would have to be swapped.. not sure if that was true or not but as they were trying to make the sale the I believe they probably weren't far off. I spent another month searching and ended up with a much nicer truck than that one for same money.

 

I don't know if modern trucks even have the option of an actual physical limited slip. They all have virtual limited slips by way of the traction control system.

 

Ram still offers a mechanical limited slip diff but is the only one left.

Ram- mechanical limited slip
Ford- selectable locker
GM- Eaton g80 automatic locker
Tundra- simulated abs limited slip
Titan- selectable locker