K&N, Flowmaster.. worth it?

Well, I have a 1996 Ford F-150 XL 300 cu. in. I've had it for coming up on a year, 97k miles on it, dead sexy and dependable. It cost us wayyy too much though, dad bought it from Carmax, and I've blamed myself for pushing him to get it. It was $8000 when it had 91k on it. I know, I know.

Anywho, turns out dad is NOT going to sell it, he's going to pay it off, so that means I can now personalize it a bit.

Do K&N air filters actually increase power/torque? Is it truly 'reusable'?

Do flowmaster exhaust kits/mufflers really increase performance, or just make it sound cooler?

If you use both together, yeah..you'll see 15-25 horsepower(roughly) plus better low-end torque. Just don't expect a tire scorching, rip-snorting straight-6 engine...it's not gonna happen.

Hell, it already spins out off a red light. that could be my crappy tires....

Ya, I'm looking for a bit more power, a bit more aggression, and a bit more gas mileage. I know I won't have a blazing fast truck, though.

Well, that would do you some good then. I saw around 5 mpg increase by hollowing out my catalytic converter, adding a flowmaster and a K&N filter.

I have an 2005 F-150 Lariat 4x4 with a 3-valve 8bubble truck. I wanted to know if this K&N would increase fuel economy and save. The truck already has 300hp, so anymore wouldn't really make a difference. The more the better. However, I want to be sure I'm getting better fuel economy. I'd certainly be interested in this product, but if my fuel economy decreases, what's the point.

Basically, my questions are:

1. Will this system increase hp? and by how much?
2. Will it increase my fuel economy? by how much?
3. Will it cause any warranty issues?

Thanks.