went through the same late8...
dealer tech dismisssed the turbos but mazda tech insisted turbo replacement..
although mine still spikes to 18psi then settles to 14-15psi...
also noticed that my mechanical boost gauge now flutters less than before..
have also installed a new catback prior to noticing the flutter so it might be a combo...
I have the same problem with my speed6 ever since I put the boost gauge on it flutters when it blows off(screwy)