I have an '03 Tahoe 5.3 2WD (105k miles) and recently aquired '05 Suburban Z-71 (76k miles), both with the original coolant. I plan in March to service both coolant systems using a Prestone Flush Kit. What coolant should I use? Licensed Dex-Cool? Other? Should I use an additive corrosion inhibiter? If so, which one? Thanks!!