You absolutely must consult your owner's manual. It will specify the correct gear oil type (API classification, viscosity, and amount). The manual will also tell you whether you have a limited-slip differential, which requires a specific type of gear oil.
Without knowing the specific model and axle configuration of your 2003 Dodge truck, giving a definitive answer is impossible and potentially damaging to your vehicle. Using the wrong gear oil can lead to premature wear and failure of your drivetrain components.