2jzgte 240sx boost problems

[Elminsster]

Sorry if this isnt the place that I should post at considering its a 2j but if anyone can help me out that would be awesome. I have an s13 with a jdm 2jzgte. The motor is 100% stock. When I got the car the turbos were set to run parallel instead of sequntial, and it would hold boost fine. I switched it back to sequential and now it wont hold boost. Itll hit full boost and then drop off to like 5-7psi. It seems to hold it well in 4th and 5th gear though. Any ideas?