I have the same gauge and IPD ecu. My mech told me 18 psi vacuum is good. I have set boost at 15 psi, but if your ecu is stock you might need to set it lower. Scott @ IPD told me their ecu runs 14 psi. It really depends on the octane of the fuel you are using. There are guys in UK that run 14-15 psi on stock ecu, but their fuel octane is 98. If you do run boost too high the knock sensors will retard timing which will decrease performance.

Have you adjusted your actuator rod?

Wills
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98 R Wagon IPD ECU, 2.5 Dual Exhaust, Dawes MBC, 94 854 turbo, IPD Goodies, 92 740 Rag Wag