Important Considerations:
* Limited-Slip Differential: If your 14-bolt has a limited-slip (posi-traction), you absolutely must use gear oil formulated for limited-slip differentials. Regular gear oil will cause the clutches in the limited-slip to fail prematurely. Look for gear oil that explicitly states it's suitable for limited-slip differentials. This is often indicated by terms like "LSD" or "Posi-traction" on the bottle.
* Check your owner's manual: The best source of information is your truck's owner's manual. It will specify the recommended gear oil type and quantity.
* Synthetic vs. Conventional: Synthetic gear oil is generally better in terms of performance and longevity, but it's more expensive. Conventional 75W-140 is perfectly acceptable.
* Additives: Some people add friction modifiers specifically designed for limited-slip differentials to supplement the oil, even if it already claims to be for limited-slip applications. However, this should be done cautiously, following the instructions on the additive bottle carefully. Overdoing it can cause issues.
In short, while 75W-140 is a good starting point, always check your owner's manual first. If you can't find it, a local auto parts store can help you identify the correct gear oil for your specific truck based on the differential's specifications.
