Dan has the right answer here... . You can install an exhaust brake on your engine but will get less than reasonable results unless you do something to the transmission to hold the pump pressure when you slow down... By holding up the pump pressure, really the pressure inside the torque converter, you locking the TC so that it can pass the power through the drive train for the engine to absorb..... Other wise the TC will slip and there will be little retarding... ... Most of the kits on the market for doing this are plug and play, and attach to the transmission computer... they monitor whats going on and will hold the pressure during slow down... These kits are usually 475 to 525 in price... plus the exhaust brake... .
The real question here... is will you use it enough to make it worth your money. . we tow with a 3500 dually a service trailer that weighs 20K lbs. . the truck has 235K miles and had its first brake job after 160K miles of towing... .