Just had an X-Pipe installed on my '04 4.4. As NCX and Pepa reported, it is subtle but noticeable - very nice indeed and just what I was looking for. I got the pipe from where NCX suggested here for $79.79 (including shipping) and had Lou's Custom Exhaust install it. Lou's charged me $63 even (including tax and a few sections of pipe) so the total for this cool mod came to $142.79 - a bargain to say the least! Two guys worked on it together - one measured, cut, bent, and flared the extra pipe that was needed while the other guy welded everything up as the pieces were made. Took the two of them 30 minutes total - I was able to do it at lunch with a little time to spare. Happy days!