Okay so here's what im thinking then as to why your car has "No Balls"
So first off, that Eprom chip is something that is used to tune your car in a way, also to save settings on. That type of chip works even when your car ISNT on. Im assuming that since your Fans run a-lot that, that chip is making them come on sooner because of that 160 degree thermo. Its keeping your engine cooler, bcuz colder air = better horsepower gains.
You have a Cold air Intake, 160 degree thermo with the fans tuned to come earlier then factory settings, also you have headers and i Highly restrictive exhaust.
I have read on here on some threads about headers that people constantly state that it is wise to get a tune when you install headers. But I think it would be wise to call up your previous owner (even though you dont want to) and ask him did he tune your vehicle for the headers as well as the fans. If he didnt, then i would suspect your headers with the lack of a tune are the reason why the car seems like it doesnt have alot of umph, and also the restrictive exhaust you have on there.
By the way, do you still have your catalytic converter and how many inches is your exhaust in width/size.