I've read a bunch of threads on misfires, but didn't find one that applied to my problem specifically. The car runs great at idle and strongly all the way to about 7.5K rpms where is breaks down momentarily before continuing up to the redline.

I did a pretty complete tune up including setting the timing, new plugs, removed/cleaned/tested the BAC valve, set the TPS, and probably some other things I am forgetting. Before I tear into and/or replace some things, suggestions on where to look for this problem would be very helpful and much appreciated.

'90 NA GTU with Bonez intake, RB down pipe, pre-silencer and muffler, A/C removed, fluidyne rad. No other performance mods.

 

check your grounds because the common 4k hesitation, one of the solution is rewiring yoru grounds.

 

Thanks for the suggestion. I've added that to my list of things to check. However, the engine winds up to 7.5K rpms strongly without hesitation, so I'm not sure that applies, but I will check it anyway.