full boost != closed wastegate.
full boost = controlled boost = wastegate partially open or even fully open for improperly sized wg.
edit: just read this part->
1) an stuck open wastegate (dumped to atm) should be audible even at idle/cruise.
2) even an open wastegate should net you 2-4psi
Do you hear the turbo (high pitch whine ~2200-3200RPM? Can you check if your turbo wheel spins freely?