The '06 was the first year that could be ordered from Dodge with an automatic transmission and Jacobs Exhaust Brake. The brake was not installed on the assembly line but was shipped in the box on the back seat floor for dealer or buyer to install. I had one I ordered as soon as I learned I could get an automatic with exhaust brake.
The eb was fully integrated with the ECM, PCM, and under ordinary deceleration the computer would close the eb then at some speed, perhaps 40 mph, momentarily open the brake, blip the "throttle" (increase engine speed), downshift to third direct, and activate the brake again. The driver could manually downshift to 2nd gear and activate the brake down to 10 or 15 mph. The 48RE locked in 2nd, 3rd, and 4th.
Even if the truck doesn't have an eb you can retrofit a Jacobs or PacBrake and integrate it engine, transmission, etc. in either manual or automatic transmission trucks.
The '06s and '07s ran very strong and held up well except for the transmissions and clutches if consistently towing heavy. Lots of performance rebuilders can make the 48REs bullet proof if you have a big credit card.
The weakest element was the manual six speeds with G-56 aluminum case and lousy dual mass flywheel and clutch assembly. The flywheels and clutches will fail at lower mileage and more frequently than the 48RE. That comment will anger some and produce fierce defense but it is true and accurate.
I put 230k miles on an '06 in one year and nine months pulling heavy trailers almost every day of its life when I was transporting and the RV industry was strong. It was an excellent truck. A lot faster accelerating than my '08 C&C and pulled very strong also.