What size belt for a T-trim 7"x 2.65"??

What belt size and brand is everyone running for this setup?
And were do you get it? I have a 0408407 belt from Goodyear, and my boost drops from ~10 to 5 psi at 5200 rpm. I'm thinking that it's because the belt is a gatorback and it's not eight solid ribs.

Please felp!!

>you can order your belts through Napa and they are Gates belts with Napa written all over them and Gates in tiny letters ;) .

I'm seeing 14 psi!!! Finally.
Of course now I'm also seeing 14:1 air/fuel ratio.

It's always something.