If I remember right the cam you have is a 108 LSA,
what is it installed at, you could advance the cam
4*-6* to pick up the bottom end torque and maybe keep
the same manifold. Also check your fuel system to
make sure its not running out of fuel in the higher
revs. Also put a vac gauge on the intake and check
the vac at WOT, you might need more carb, more than
likely