I need to service the radiator fluid on 3 GM's. 2000 Silverado 1500 5.3 with under 50k miles. 2003 Tahoe with 98k miles. 2005 Malibu Classic 2.2 with 55k miles. All have the original fluid. I want to use the Prestone Flush kit with the attachments for a garden hose to flush. Which fluid should I use? Dex-Cool or Peak Long Life? Other recomendations. In all three vehicles the fluid does not look dirty. Does Napa still make NAPA KOOL and is it compatible with Dex-Cool? Thanks.