Having owned a '96....'01 and my current '03 Cummins with 320k+ miles I wouldn't own a 5.9 Cummins without a Exhaust brake towing anything or empty.
My current '03 5.9/NV5600 has the Jacobs exhaust brake which was installed under Dodge Businesslink program for 395 bucks when the truck was new. Its been flawless.
The Jacobs with the manual 6 speed tranny is heaven to operate.
I did the first brake job at 180k miles. All it needed was new pads as the rotors still had OEM machine marks in places.
The manual tranny allows the exhaust brake to work in all gears including reverse. And its a great cold morning fast idle warm up feature especially when the wind shield has hard frost.
The Pacbrake with the aux remote air pump would be my choice for adding to a used 5.39 Cummins. It also has the fast idle warm up feature. Great option.
Keep in mind a exhaust brake needs more rpm to get more braking. I've found 2400-2600 rpm is all my rig needs with 11200 lb trailer pushing me down a grade ie; Wolf Creek Pass.....Monarch Pass.....I-70 in CO.