12 psi would be about normal for a 150bhp car that isn't chipped/remaped, the 180's run 14 psi (from memory) with chipped motors running between 18 and 22 psi. 5 psi sounds like limp mode.. possibly overboosted at some point. Disconnect the battery for 20 - 30 minutes and then take it out and drive it hard, see if it makes a difference.