Have put cold air kits on almost every truck and SUV have ever had except for our 2008 Tahoe Hybrid. Just did not feel the need on that one. Twenty one plus mpg overall with 120,000+ on the odometer now. Always noticed at least .5 mpg improvement, most of the time more. Just bought a brand new 2015 Silverado 4X4 and am thinking of adding a cold air kit to it at some point. Just waiting to see what the cylinder deactivation and six speed tranny will average for a base line. The best system ever for me was a VARA-Ram I put on my 2004 Corvette. Huge performance improvement and 2.4 mpg highway mileage improvement. Expensive, though, at $750 installed.