I have a 1996 VR4 and here is whats done to it
3sx downpipe, test pipe, borla rear exhaust.
Upgraded Taylor wires
open air filter
BOV set up like factory not open atmosphere
forget which spark plugs but they are new good quality ones ( I will have to check and see which ones)
gutted one pre cat so far haven't done the rear yet ( not sure if this is the cause of the problem )
That's it under the hood.

when I hit 4k it sputters then its fine. seems to do this through the first few gears. Don't have anywhere to test it any faster.