ok, i have a lean in the rear of my truck, i dont know if it is a worn shock, leaf spring or what, i was told by some one who said they worked at ford but he had no clue what he was talking about but he said i could add a spring and or a leaf instead of swaping the whole set up and also he said that if i replace one i must do both...

need some real help,

 

left side tire to rear fender is like 3 inch and the right side is like 7 what could the lean mean

 

if one side of your truck is 4" lower than the other then somethings majorly wrong.

theres tons of things that could be wrong.
the easiest way for us to tell would be to take a pic under the back of your truck.

 

its probably a broken leaf spring, take a look and see if one of them has a crack in it....you can usually get a spring pack at a junkyard for 50 bucks...less if you pull it yourself