Turbo Celica GT bogging down in 5th gear

I've got an 01 GT and it has a Garrett GT2860rs turbo kit from turbo kits .com and a greddy emanage system. When I'm cruising around not boosting much I can go all day without the bogging feeling but when I'm playing and boostin 12psi then say I get on the interstate it bogs down badly for a minute then pics back up. I'm wondering if its a tuning thing or if maybe its my dual stage bov. Anyone had this prob?