I'd use one that doesn't release boost pressure, but just regulates what boost pressure the MAP sees, like ITP's. ITP's is popular for that reason.
I'm also relatively sure the PCM doesn't consider it "overboost" until 22-25 psi, not 19. I may be wrong though.
Paul
Kinda why I said 19ish. Every 7.3 MAP can be a bit different. This, more than stock boost thing can get to Rocket Science.. purdy quik. The term: Everything is Relevent.. applies.
JMO but, we need to look at the MAP Sensor And.. Waste-gate Actuator. You can trick the Map sensor into not seeing over-boost, but at WOT or a real heavy, lenthy demands, like Towing.. EXhaust gas pressures (negative pressure) can actually [help] Pull the waste-gate open.. IF the Actuator spring/rod has'nt been tightened, to compensate for that.
Most stock actuators can be tightened/adjusted Some, but not much. Some are not adjustable at all. (crimped)
I went with a Banks, Big Head Actuator, from a Site Vendor. Fully adjustable.