I installed UD pulleys (Moto Blue) on my parent's 04 5.3 Chevy Avalanche (stock with the free mods) and it was a noticeable difference in acceleration. Even my mother of all people noticed the difference. Then they drug their bike trailer to North Carolina from Texas and the gas mileage increased. So a noticeable increase in acceleration and gas mileage. It was never dynoed so we cannot measure the gain, but like I said for my mother to notice a differnce, then there is something to write home about.
