What's the difference?

Is it just the transmission or is there something else?

 

Standard/Delux/Premium in the case of the mustang is more or less trim levels.. i.e. leather, stereo upgrades, trim packages, "the higher the package, the more creature comforts/appearance items". The drive train (besides wheels anyway) does not change, although I mostly see Premium Mustangs w/automatic transmissions, but you can get a premium package mustang w/5-spd...