Just bought a 5.7 for my Duster

you are correct. But you will need the correct throttle body, and you will need to add in egr as the 03 did not have it and you willl end up with a code for it. Now if your not worried about emissions then this is not really an issue, if the egr does not function it's just a light

If you get the ECM flashed, I'm pretty sure they can program out the EGR.