If you stay below 3k rpm, the more effective mods are going to be an upgraded muffler, and take care of the decrease in diameter by it, and a ported throttle body. A better flowing drop in might help a little. These things don't make a better run out to the dragstrip change. They make it a little better down low, but that's what you're looking for. 4.10 gears also help a lot in the low range. They get you up high though. My interstate milage dropped from an average of 24 to 20 mpg when I went to 4.10's. My 45-55 mph is still around 24 mpg though. City is only 12-14, but could probably be up to around 15 with a different driver. The cones can help if you make a lot of other changes, and figure out a way to get a ton of cold air to it. I've had the best luck so far with a hood that dumps cold air into a K&N heat shield built up to seal against the hood better. I removed the little air dam so additional air would get to it from under the hood. Also, the normal air that gets to it around the radiator comes in. All this creates a high pressure cold area at speed, and a good source of air even at a stop. You can actually feel it pulling in a little air through the scoop as it idles. I found that better economy actually comes from leaving the bottom of the heat shield unsealed. I guess it adds a just enough gas to the slight increase in pressure to be noticeable. I've found that to get around a 5% power increase from ram air, you would need to be traveling at around 160 mph to create the 1 psi you would need. There are ways to create that additional pressure, but that discussion tends to start flame wars.
