Sounds like 03 and 04 have the pedal converter and later years use the electric pedal without cable. So you have your choice, use the electric pedal or rig your stock pedal up to the pedal converter box. Also if you're running an older style auto trans, you'd need to rig up some kind of a kickdown linkage.

The only other low-cost option I've heard of for the modern hemis is the megasquirt efi controller. However you'd have to wire it all up yourself and tune the motor yourself and set up the 5.7 with a conventional cable driven throttle body. Sounds like you're probably better off working with what you've got.