An intercooler on a diesel really keeps egt's down and allows you to push harder. There's a benefit. But at elevation the only thing you can do is make more power.
Not usually. They're at 6. And usually an hour or two from my house. I work nights and am not up early enough to make it. Plus the thought of fighting Seattle traffic is unappealing.
I attend most of the north sound cruiser meets
before you start trying to replace the rear stuff I recommend seeing how bad the hard lines are, and if they're bad just replacing the whole setup with gates hose.