Hey, im newer here, but i decided to take my GTP out for one last stroll before winter, and at about 80 or higher, The boost would be lost, to about half way, going up and down which in turn slowed accerleration down alot. Wondering if this is a sign of knock retard, or what could cause this? New belt on the sc already.(3.4 pulley on car) Planning on new headers over the winter to reduce KR. Any suggestions on all this? Any help appreciated, Thanks>