Originally Posted by NWRQC
I noticed very little change in mpg until I added the third piece to my set-up. First was the intake (spectre), louder and no mentionable change in power or fuel economy. Second was the Programmer, decent bump in power and very minimal change in fuel economy. Worth the money spent. Third was the exhaust. I replaced the muffler with an 18" Magnaflow and removed the resonator (3" tailpipe). Once again a decent bump in power and noticable mpg increase. I think once I added the exhaust it allowed the intake to reach it's potential, and same for the programmer. They all work together and compliment one another. Ive seen an increase of a solid 8% around town and still figuring out the highway mpg (I dont drive my highway). All in all 8-10% increase.
I would start with replacing the muffler and removing the resonator. Keep the piping you already have. Then find a good deal in a CAI.
As was said all 3 working together is the best. A good muffler will likely do some, as well as a new intake or programmer. I would say the programmer is the place to start, by increasing the efficiency of what you already have. The other 2 together at the same time is probably the best way to do it. What goes in has to come back out. The trucks are set up to work in an efficient, yet cost effective manner from the factory. Putting on some sort of CAI along with a decent muffler would help as a combo also. Another over-looked often times one is the Y in front of the muffler, (atleast on the 3G, idk about the 4G as I have an 05). A much better Y at this pinch point has potential to do wonders!!