Boost problems only goes up to about 15psi and starts to lose psi at 5000 rpm.
I have a 2013 abarth cabrio with 80,000 miles. Bought an exm from 500 madness about 6 months ago . So my car will sometimes fly up to 18psi but does not hold at 18. It lately was only staying at about 13 psi with the ecm then after a few seconds it starts dropping all the way down to 6 psi . It seems to drive a little better as far as higher psi of about 15-16 psi with the bypass in in 4th and 5th. But still starts dropping in forth on freeway at 5000 rpm .I got it to hold 15psi in 5th gear for a while longer. We have tried my mans 2014 abarths actuator doesn't seem to make much difference maybe instead of 13 psi it goes to 15psi with his actuator and the ecm in. Held 15 psi with his actuator and the bypass in. Next we are check the actuator solenoid. Any ideas help ? Does the turbo lose power at 5000 rpm if the turbo is going out . Or could I have a leak somewhere by intercooler piping. His 2014 gq abarth with the ecm goes to 18 psi and higher . Actuator looks newer than mine his car has a cold air intake and 500 madness ecm as well

I think a boost leak, hoses, intercoolers, clamp's.