Modifications and replacements of components in a vehicle's differential and rear axle assembly, aimed at improving performance, durability, or traction. These upgrades can include installing limited-slip differentials (LSDs) or locking differentials to enhance traction in challenging conditions, upgrading axle shafts for increased strength, or changing gear ratios for improved acceleration or fuel efficiency. Such upgrades are often sought by off-road enthusiasts, performance drivers, or those who tow heavy loads, as they can significantly improve a vehicle's handling, power delivery, and overall capability.