The 2004-2007 5.9 Cummins trucks can all run an exhaust brake with the factory ecm. The 04-05 trucks need custom tuning to make it work right and the 06-07 trucks already have the tuning from the factory to run the brake.
Also the lockup and shift schedules can be modified to greatly improved the 48re towing performance. My truck will lock in manual 2nd at 25mph. Also in drive it will now lock in 3rd and hold lockup shifting to 4th. The 4th gear shift has also been remapped to happen at a far better road speed than stock. My tow haul button has been changed to an overdrive off button which is perfect for long steep climbs in locked 3rd and the lockup stays locked now even when coasting in 3rd.
Anyone interested in getting this tuning get hold of
https://www.mm3tuning.com