SR20DET cutting out when nearing boost

[iGreek]

Just got my redtop SR20DET running. 370s/S15 T28/stock maf. Wouldn't start because of a bad cas.

Now I have a problem of it cutting out/misfiring when it gets anywhere near boost. Revs fine in neutral until it hits about 0-1 psi of boost. Then it starts cutting up. Same as when trying to drive. It cuts out when it gets anywhere near boost.

Vacuum is at 21 hg and I've read that it is normally around 18-22 hg; so that seems fine and leads me to think that there are no vacuum leaks. Double checked all couplers and I don't think it's a boost leak. Adjusted the timing and got it to run real nice at idle; sounds very smooth, unlike the cam-like sound it had before.

Is it possible that it is the spark plugs? They are quite black. Would they cause such a big problem or a cut/misfire? If so, should i get NGK BRK7Es and what gap should I set them at? Thanks.