I recently bought this 5.7 charger with 180k miles on the odometer and 50k on the new engine and it runs perfectly but for some reason every code imaginable is being tripped. If you reset the ECU it all comes back immediately, the seatbelt light is always on and dinging too. the man i bought it from had engine swapped it to one of the same size, not sure if this could be causing it.

it has custom subs in the back that have been wired by a professional

 

I would say a combo of the actual engine swapping process and the custom wiring; whenever wiring is messed with be it on purpose or accidentally (like moving harnesses to remove/install engine) there usually seems to be issues.