Anyone have experience improving the fuel effiency. This is a chip advertised on this website and many on e-bay. I have checked with buyers from e-bay, and those that replied siad those were useless! I love my thrucks, but some additional miles per gallon would be awesome! A little extra horse power would not heart either. I have a 98 K1500 5.7L Surburban and a 2004 AWD Yukon Denal XL 6.0L I look forward to reading your replies.