300zx flaring revs when turbos kick in?

Sounds like a worn clutch disk or bad pressure plate. You mean a 1990 300ZX tt made in 1989 right? How much boost does the gauge say under the spedometer? some times the boost actuator hoses crack and all a sudden you have over 14 psi boost and slipping clutch. A word of warning a well worn stock engine will only take 14 psi boost a short time before connecting rods come out of the motor. Good Luck