Anybody know what this is? I just saw it listed on the window sticker for a couple of 05 GT's.

 

Howdy - Looks like the 54V is probably the sport appearance package (i.e. Spoiler for the GT). You can download the file with the link below and look up the optional components on p27 (that is, page 29 of 37 in the acrobat document, but it's page number 27). Kinda neat, because it lists their weight, too.

2005 Mustang Specs

Hope that helps -