You never mentioned any work done on the fuel injection - fuel pressure changes, chip changes, injector changes, etc.

You have modified the motor to draw more air, and unless you modify the fuel system to flow more fuel, you will have problems (too little fuel fot the air - so too MUCH air, so to speak)

the flat spot at 4500 is an indication that your fuel curve is off.

If you don't understand TBI, you don't want to go farther with TPI, etc. The systems work on the same principles, so you gotta know the basics first - you can't diagnose it unless you know how it works, or is supposed to work THEN you can decide what is NOT working as it should and then you have your FIX.