new turbo =weak jake

nothing you can do about it sorry, the aftermarket turbo I put on mine has a smaller housing than the stock turbo A/R 1.23 against the stock 1.39 and my jake also lost about 5-8 psi on engine braking.
Lucky I have a brakesaver and just turned that up a little.

 

I put the same turbo on my truck recently (it was actually a 478120, but I've been told that's just the new part#) and was told beforehand I would loose some jake power. I rarely go west of I35, so I don't have the high mountains and thin air to deal with like you probably do, but I've found that if I grab another half a gear and let the engine run from 17-2100rpm or so instead of 15-1900 like I used to, it seems to work a little better. I also turn the fan on now on long grades, which you probably already do.

 

Did you ever get your boost up?

 

You can put a exh brake on if you want, mbe4000 mecedes come with them from factory

 

My Mack has what they call a 'stealth brake' which is an engine brake in conjunction with an exhaust brake (it sounds like a wet fart), most likely because their regular engine brake sucked so bad. It seems to work fairly well, but it's no big block jake. It's weird in that it doesn't build any boost like a normal jake.

I believe there are stiffer exhaust valve springs in the head, but don't quote me on it. They did this only for a couple years however, mine's a 97 and I think in '98 the different engine series came out and did away with the exhaust brake end of it.

 

You could do it, It will help... not sure if it will be enough for what your looking for. Won't lose power with it or anything