What kind of transmission fluid should be used for a 2003 Chevy 2500HD?

The type of transmission fluid recommended for the 2003 Chevrolet Silverado 2500HD varies depending on the type of transmission installed. For automatic transmissions, it is advised to use DEXRON-III Automatic Transmission Fluid. If your truck has a 5-Speed Manual Transmission with Low Gear, opt for GM Goodwrench Synthetic Manual Transmission Fluid or an equivalent SAE 75W-85 GL-4 gear oil. For the 5-Speed Manual Transmission without Low Gear, the recommendation is SynC-HRomesh Transmission Fluid or an equivalent. The 6-Speed Manual Transmission with Low Gear should use TranSynd Synthetic Transmission Fluid or an equivalent. These fluids meet GM's requirements, and it's important not to add any treatments or additives as they could harm the transmission. To prolong the transmission's lifespan, it is suggested to change the fluid and filter every 60,000 miles.