Boost problems

So I'm having problems with my boost. Under somewhat hard acceleration I'm usually boosting around 17psi, but sometimes in 3rd gear or higher, when I get to about 5000RPM the boost suddenly drops and won't go above 5psi. If I turn off the car and restart, then it boosts just fine.  

Hopefully I explained that good enough, any ideas?

Could it be the N75?

Have the car scanned the next time it does it.  Should be something in there since it puts you in soft limp