Running straight pipes is not a good idea on the computer controlled vehicles. Not only will you be losing back pressure (thus losing power), you'll be throwing codes left and right. And the factory tune will be off greatly. On a carb'd motor, it was not so bad, but with computers and controls, it is not a great idea.
You'll be better off with just replacing the stock muffler with a Flowmaster, Magnaflow, Borla or other brand. Though, you'll be even more better off with a cat-back exhaust system.