check fuel pressure and the back pressure from the cat converter. Since you have ruled out the three major components that make up engine performance, there simply isnt much left to look at.

Here's a couple guides to read, they will help you figure it out

https://www.2carpros.com/articles/engine-has-low-power-output

https://www.2carpros.com/articles/symptoms-of-low-engine-power


Roy