Weird KA issue, please give me some ideas

[OkiDori17]

So first off I've been searching and working at this for months. I'm a fairly good mechanic and can usually diagnose easily and quickly, but this has me stumped.

Buddies stock s13 ka, super slow. It doesn't bog or sputter, just has no power until high in the rpm (about 6500 ~ almost redline) then it'll take off like a rocket.
All sensors have been replaced. Timing has been set twice now. 2 different timing guns both have it perfectly at 20 degrees tdc. Only code it's throwing is 34 (knock sensor). Replaced with brand new one as well as a known working one from another car, known working loom replaced as well. Still throws the code. No vaccum leaks. No fuel issues. Spark is good. ECU replaced.
I'm lost.

All you KA gurus give me some ideas to look at next.
Friend is wanting to sell car, but I'd feel horrible knowing it was still messed up like that.

Any help is appreciated.