That is very common behavior, if the factory wastegate solenoid is still hooked up and functioning.
Look to see if your wastegate actuator is adjustable. Meaning, if the rod that connects the downpipes' swing valve has an adjustable turn buckle, then you can switch your setup over to
"Tuner Style". If you have the wastegate solenoid on the passengers side valve cover hooked up. (OEM stock configuration in picture below)
What you do is take all of the turbo to wastegate to solenoid hoses off. Including the grey T and the black 90* elbow at the solenoid.
These hoses you see on this TA-49 turbo.
Keep the solenoid electrical connector hooked up. Now, take a single piece of vacume hose, cut to length and run it from the 90* brass barb on the turbo, down to the hose barb on the wastegate actuator. Don't forget to zip tie all the hoses. From here, you adjust your wastegate actuator to static position. Meaning, adjust that turn buckle so that the swing valve has just enough tension to keep it closed. See this picture.
If you have a stock spring'd wastegate actuator, this should net you 12-14psi, depending on ambient conditions. From here, you can either manually adjust your boost higher by tightening or shortening this adjustable turn buckle. On a stock spring'd actuator, one complete revolution (2 half turns) of the rod should = 1 psi of boost. If you have a heavy duty actuator your boost level at static would be around 18-19 psi. We can typically get away with running 16-18psi on todays craptastic pump gas if your fuel system is up to snuff.
Fuel pump, hot wire kit, adjustable fuel pressure regulator and a good 93 octane street chip.
Hope this helps.
Patrick