7.3 what enging brake would suggest ...
There are two kinds of exhaust brakes - the cheaper "electronic" kind, and the over-$1,000 mechanical kind.
The electronic kind does a decent job for trailers that weigh up to around 8,000 pounds, and it will help at least some with heavier trailers. There are two versions of the electronic exhaust brake.
The least expensive is the DP-Tuner Decel tune. It's used only for coming down the mountain, so it won't work with a programmer or tuner - you have to have a "chip" with other tunes on the chip. The switch to the Decel tune at the top of the pass, then back to your towing tune at the bottom of the pass. The Decel tune costs only $40 if you already have the chip.
F5 1-16 Position Switch on the fly Chip - Chips - Tuning - 1994.5 - 2003 Powerstroke 7.3L Truck - Ford Powerstroke
More expensive is a plug-in model such as the BD Brakeloc.
BD Power - Product: 7.3L BrakeLoc
The better (and more expensive) exhaust brakes have their own butterfly valve they use to stop up the exhaust pipe and retard the engine. They're made by PacBrake, U.S.Gear, Banks, BD and maybe others. They all cost over $1000 MSRP. Here's the BD version:
BD Power - Product: Exhaust Brakes
I had an electronic exhaust brake similar to the BD Brakeloc - cost around $400 for automagic tranny, or $200 for stick shift. (The automatic has more programming to lock up the torque converter so the engine stays locked to the rear axle.) The seller has sold out to a bigger outfit, so I won't link to that one, but it worked great.
and are they hard to put in?
The "real" exhaust brakes are not very hard. You have to install the butterfly valve in the exhaust system, and hook up some wires and a switch on the dash. Here is a link to the BD Exhaust Brake for a 7.3L. Decide for yourself.
The BrakeLoc is even easier, because it uses the EBPV that's already installed in your engine. And the tune is easiest of all - provided you already have a multi-position chip installed. If you don't already have a chip, then you'll want one so make that your next mod:
Chips - Tuning - 1994.5 - 2003 Powerstroke 7.3L Truck - Ford Powerstroke
I have that tune too but doesn't seem to do anything. Ended up not even using it at all
Then you probably didn't understand how it works. The DP-Tuner Decel tune does a good job of retarding the rig, but only when a heavy trailer is pushing you down the mountain at a faster clip than you want to go. Under those conditions, downshift to maintain the engine RPM between 2,500 and 3,000 and you will definitely get some retarding - assuming your exhaust back pressure valve (EBPV) is installed and working properly. If your trailer weighs less than about 8,000 or maybe up to 9,000 pounds, you probably won't even need to use the brakes at all to maintain a safe speed around 65 MPH.
At any engine RPM less than about 2,000, it won't do much. It begins working at around 2,000 RPM, and doesn't really go to work until 2,500 or so RPM.