If it's spiking when it comes on boost then it's likely your SET GAIN is too high, the gate is being held closed till too close to your target boost setting. Try lowering it slightly.
I managed to get rid of a hesitation my car had when it came on boost by lowering the SET GAIN by 0.2psi, now it comes on just as strong but is smooth as.
If boost is tapering off you need to play with your GAIN setting, do this slowly, a couple of % at a time.