Yeah, stock ECU might go into Rich & Retard if you go much above 10psi.
Turbo may handle 12psi, may Blow at 7psi... Luck of the draw.
Sounds like it may be going up to 18psi so I would be trying to set that sucker around 10psi and see if the problem stops.
Could also be partially, Sparkplug / gap & old coil related too. (or a combo of all this)
Sell the EBC and buy a 10psi Rb20 actuator.
profit???