I have an external wastegate with a 7.25 psi spring in it. According to my boost gauge I'm boosting to 7.5 psi. The wastegate is getting boost from the compressor housing and the boost gauge is reading boost from the manifold.

Can boost creep only build up to a certain point and then level out?

 

Its possible due to pressure lost at the intercooler if you're getting the signal from the tubo housing and your boost gauge signal is from the intake manifold.