setup im taling about was stock cam and stock rpms range.
Dual springs should be changed every 10-15k miles if used with an aggressive cam or alot of boost pressure
AR will also effect back pressure a 81 would make sense for your high torque number and lack of HP, if you can measure back pressure preturbo it would tell you if that is your issue. .96 will deffently help carry further out, sharp bends in the exhaust will also hurt some but probably not enough in your case.
what are specs on cam?
you can encounter valve float if you have to much back pressure, your cam along with small AR can be hurting you. Some say overlap is bad but to much neg over lap will shorten your RPM range. I prefer some overlap since it carries alittle better. Makes nicer for topend power