Is it possible to put a engine brake on a 04. 5 with a 48RE automatic?
An engine brake uses a change to the valve train operation. It is an expensive and complex system not available for Dodge Rams.
It is possible to add an exhaust brake to your Cummins engine but it will quickly destroy your automatic transmission unless you also purchase and install an aftermarket method to lock the torque converter of your transmission when the exhaust brake is applied.