The 3rd and 4th gen can use the 2.5 inch in and out center offset, i went with 3inch so it can be louder for me, but the 2.5 will be fine. Muffler shops here charges 70 for install, but my camed out to 170 since he charged me for the custom 3 inch pipe, starts from stock flange on the y pipe, then one 3 inch pipe to the center of the muffler, the out on the offset where a pipe is bend to go up and over the rear axel and back down to the side, i have it out on the corner of the bumper, as u can see on the vid i posted, it makes my truck look better. All my stock muffler and pipes were not used, except the flange where he cut off to weld the new pipe onto.