1987rx7t2

i have an 87 tll wil rb downpipe, high flow cat and cat back exhaust, blitz cone filter. and i have a leake in the urbo manifold, but ordered a hks turbo manifold, but the car has 112000 miles on it and runs stroung, until about 45000 rpms, in first gear its fine, second and up arround 4500 rpm the car has no power and sounds like it does not want to go, i have to shift at arround 4000, even when hitting the accelerator hard, need help!

Cosmo Donk

Fix the exhaust manifold leak and then tell us what is happening.

Also vacuum leaks.