Rich and Retard occurs when the Air Flow Meter detects too much volume of air traveling through it and thinks the turbo is possibly overboosting, it than Richens the fuel and retards the timing (this causes it to lose power), essentially a safety feature to try preventing you damaging your car if something goes funny with the wastegate..
Most likely a) you have a turbo back exhaust and the boost is now up at 10/11psi, because you go full throttle it overboosts slightly which could trip R&R..
Get an SAFC or turn your boost down..
OTHERWISE.. it's your coilpacks breaking down at 4,500 rpm like everyone elses, common in R33, not so much in R34.. This can be noticed as you might lose boost and it stutters/missfires than picks up again..
Sewid, you agree?