LegacyGT2.5L

Also, is this my only concern? Or should I be worried about some thing else being my problem.

I recently had on my new Legacy break down on me and after fixing it I have discovered that I have lost four psi in my boost, I have a gauge on the dash and it usually read at seven psi but is now down to three psi. I was told to check some vacuum hoses but I’m not sure which ones to check, any advice?