I assume that you did this with the vehicle stationary. As such, the turbo cannot produce much boost, if any, because the engine is not sufficiently loaded. Therefore, this would be a poor test to determine if the turbo is performing satisfactorily. Your previous result of 6 psi does show that something is amiss, provided that you got that result with the engine under full load (vehicle moving) with the rpm above 2500.

In this case, I concur with the previous posts whereby the wastegate is likely to be the primary culprit. There is no need to spend a lot of money rebuilding the turbo unless it is absolutely required.