I believe the 09 5.7 is rated at 390 hp in the Dodge Ram only.The Challenger/Charger is rated at 372 or 375 I believe depending on auto or stick.It would'nt make much sense to have only a 35hp spread for the added markup of an SRT-8.
I believe the intake and camshaft are different as well as the bottom end is stronger on the SRT-8 to handle the extra rpm.