When was the last time you changed the fluids in your auto?
"RB20DET running 10psi fuels up really bad after 4000rpm or so and u can even see black smoke pouring out the exhaust!"
I do not really understand? My Stang runs 40psi at idle, and about 90-100 under boost. Sounds like your fuel pump is going, your psi is not there at the higher rpm range.
Black smoke sounds like your turbo might be going as well. Just a guess, all your problems seem to be unrealated, meaning you got some work to do
Good luck.