Ls vs positive traction

Hey everybody i thought i would share this experience to make sure there are no flaws in my logic. I went to an auto shop today to ask how much it would cost to install a detroit trutrac ls diff. The mechanic told me that my truck probably already had a ls. I told him that it was an open diff and he asked if one wheel was in the mud and the other was on pavement if the one in the mud would spin. I told him it would. apparently this was proof that i had a ls. Then i told him that this ls was supposed to offer partial lock up and he told me that a locking differential was i device to keep you from burning up your differential. However he did tell me that positive traction was great. They are the same damn thing are they not? But he said that even if i didnt have a ls already he probably couldnt install one because it would throw codes. How the fuck would the computer system know when there is no sensor to tell it that? Please tell me if im wrong about this stuff but im pretty sure he was. Thank you

 

I searched for it earlier and it hadnt showed up on the threads started by me page. sorry

 

That mechanic should never be allowed near your truck again!

 

thats what i told my mom. He overcharges so much but she loves him for some reason