I installed a Pacbrake on my 2004.5 Dodge 3500 48RE auto about 2 years ago and absolutely love it. They make a specific version for the (pre-2006) auto which includes a trans controller that handles the lockup. It works great. There's also a toggle switch with LED that lets you turn the EB off and tells you when the TC is locked when it's turned on. I leave mine turned on all the time.
Coming down the Sherwin Grade (a 20 mile 6 percent grade on CA395) used to fry my brakes by the time I reached the bottom. With the Pacbrake, I don't even have to touch the brake to maintain a comfortable speed. In fact, I have to speed up occasionally. I won't ever tow heavy again without an EB.