I saw this on another forum but was hoping someone here might have insight. Apparently on 12/12/2011 there was a change in the piston design. Here is the first listing on the ford parts site:

Engine Piston
5.0L V8 32V Dual Over Head Cam EFI Modular ; Standard, Refer To Workshop Manual For Proper Grade Selection, Piston Only; Wrist Pin And Retainers Must Be Purchased Separately
$83.66 Select a dealer for prices & availability
Vehicle Build Date before: 12/11/2011


And here is the second:
Engine Piston
5.0L V8 32V Dual Over Head Cam EFI Modular ; Standard, Refer To Workshop Manual For Proper Grade Selection, Piston Only; Wrist Pin And Retainers Must Be Purchased Separately
Call Select a dealer for prices & availability
Vehicle Build Date after: 12/12/2011

There is no pricing listed for the second revised piston, it just says "call". Does anyone know exactly what changed in the new design? The site can be found here (just search for piston):

http://www.fordparts.com/Commerce/Ca...Mustang#Search

 

I read that there was a change in the 5.0 GT motor.

 

Probably related to the deletion of Piston squirters on the regular 5.0. They are now using similar sleeving of the pistons in the base 5.0 as in the boss I believe.