Exhaust Brake
I've used the US Gear D-Celerator for 3 or 4 years, now, pulling 6000 lb TT in the Rocky Mountains. Works great. No need to change exhaust valve springs. Simple to install ($25 at the muffler shop to cut and weld up the flanges to the exhaust pipe) Also, I like the idea of the butterfly being a long ways down the pipe from the turbo exit... those with the butterfly in the turndown elbow have got to increase backpressure when open.
Added bonus: Makes "servicing the cat" a breeze, if you so desire.