what does it do in neutral at that rpm?
and what do the leading edges of yer turbo compressor wheel look like ? are all the I/C boots tight'n in good shape* ? including the intake boots, from the Y pipe to the intake plenums ?
*FWIW, I've seen I/C boots that had stress cracks in'm. They're not split open, just cracked.. to the point where as pressure builds to a unknown psi, they leak/bleed off >Some< pressure.. but not all.
Give All the boots a halfa turn tight ?