Many consider the 1994-1998.5 5.9L 12-valve Cummins engines to be the best due to their mechanical simplicity, lack of emissions equipment, and long-term reliability. These engines are known for being easy to work on and modify, making them a favorite among enthusiasts, especially those swapping these into other vehicles. The challenge today is finding low-mileage units, or the expense of rebuilding these older powerplants. Other challenges include known design weaknesses in the trucks themselves, such as broken dashboards and interior trim that is easily broken and hard to replace.

With basic tuning, you can expect 100-150 horsepower gains on most 5.9L and 6.7L Cummins engines. Adding performance parts like larger turbochargers or injectors can push the power even further, with potential gains of 200-300 horsepower when done properly.

Increasing your Cummins-powered Ram’s towing capacity involves a combination of performance tuners, turbo upgrades, and suspension enhancements like lift kits or air springs. Upgrading your transmission or adding transmission coolers can also improve towing capability and prevent overheating under heavy loads.

The 5.9L 12-valve Cummins (1989-1998.5) is widely regarded as the most reliable Cummins engine due to its mechanical injection system and lack of emissions equipment. Its simple design makes it durable and easier to maintain over hundreds of thousands of miles.

The Aisin AS69RC automatic transmission, found in newer 6.7L High Output Cummins models, is considered one of the strongest transmissions for handling high torque and towing heavy loads. For older models, the NV5600 6-speed manual and NV4500 5-speed manual are also highly regarded for their durability and performance.

The 6.7L Cummins engine has several common issues, including EGR cooler failures, DPF clogging, and turbocharger wear due to excessive soot buildup. Regular maintenance and performing EGR and DPF deletes (where legal) can improve reliability and performance.

The 6.7L Cummins offers more torque and modern emissions controls, making it ideal for heavy-duty towing and meeting stricter regulations. The 5.9L Cummins, particularly the 12-valve, is simpler and often more reliable long-term, with fewer emissions-related issues and easier modification potential.

Yes, DPF deletes can improve performance and fuel economy by eliminating the emissions system, but it's important to note that this is illegal in many areas and can void warranties. Be sure to check local regulations before proceeding with a DPF delete.

To improve fuel efficiency, consider installing cold air intakes, high-flow exhausts, and performance tuners to optimize the engine's airflow and tuning. Regular maintenance, like cleaning the EGR and ensuring proper tire inflation, can also help improve fuel economy. Earlier 5.9 Cummins two-wheel drive trucks can easily see fuel economy in the 24-25 MPG range.

After upgrading your Cummins engine, regular oil changes, fuel filter replacements, and cooling system maintenance are essential to ensure reliability. Consider upgrading the transmission to handle the added horsepower and torque, especially if you've added performance tuners or turbo upgrades.