I have a2000 Silverado 2500 non-HD 6.0L Gas. I dont exactly have the money to go out and buy an expensive exhaust system so i wanted to comprimise. The other day i drilled about 1/4" holes into the rear or my muffler. i sounded like a race car when i punched it just not as loud and it gave it a deeper idleing tone. well it also decreased my gas milage. my truck has 212,000 miles on it. i get about 6 MPG. but i was thinking about stright piping it. just the muffler not the CAT's. will this sound good or should i take the CATS off anf leave the muffler OR should i take em all off and buy a Flowmaster 44 muffler and striaght pipe the rest? im looking for advice on what would sound good and what would give me better or less gas mileage. Any Advice?

p.s. my exhaust is stock right now.