The 6.7L inline-six Cummins engine has been a rock-solid performer for years, but for 2025, Cummins has re-engineered major components to improve power, reliability, and serviceability. After more than forty years of upgrades, Cummins continues to build better, and the newest 6.7 Cummins in the Ram trucks really is a completely new design with a LOT of well-thought-out upgrades.

Unified High-Output Design

In 2025, there’s no more choosing between standard and high-output. All Ram HD trucks with the Cummins 6.7L now come with a single high-output version:

• 430 horsepower
• 1,075 lb-ft of torque This power level matches or exceeds earlier HO configurations and is now standard across the board.

Engine Block Goes Back to Cast Iron

In past years, Ram used Compacted Graphite Iron (CGI) for the engine block—a strong but sometimes brittle material. For 2025, Cummins reverted to a cast iron block that boosts durability and better withstands long-term heavy use.

But this isn’t just a material swap. The block has been redesigned to accommodate:

• A new cylinder head
• Top-feed fuel injectors
• Glow plugs instead of the old grid heater

This redesign makes the engine stronger, smarter, and easier to service.

Bye-Bye Grid Heater, Hello Glow Plugs

The 2025 Cummins 6.7L ditches the grid heater, which had been an incredibly solid performer until recently, when a history of bolt failure and cold start concerns began impacting the 6.7L. In its place for the first time ever? Glow plugs! Ram and Cummins assure us this system will:

• Heat faster
• Start better in cold climates
• Eliminate one more common failure point

This change also made room for a better airflow path and intake redesign we’ll touch on further down.

New Turbo, Same Holset Reliability

Cummins stayed in the family by upgrading to a new Holset variable-geometry turbocharger (VGT). For those of you who don’t know, Cummins does technically own Holset, but this refreshed design includes:

• A new compressor housing
• Heavy-duty bearings
• Faster spool time for better throttle response

Although Cummins hasn’t published boost specs yet, we know older models hit 33+ PSI. This new turbo is built to handle more.

Aluminum Intake Manifold

Another efficiency move: the heavy cast-iron intake manifold is gone. The 2025 engine features a lightweight aluminum intake that improves airflow, lowers weight, and helps emissions. We’ve got our concerns about how this will hold up under high temps, especially given the differing expansion ratios of the two metals (the lower plenum intake fiasco of the pre-Hemi 360 gassers comes to mind…)

CP8 Fuel Pump and Top-Feed Injectors

Cummins replaced the controversial CP4.2 with the new Bosch CP8 fuel pump, and they’ve been addressing the weaknesses of the CP4.2 for several years. Bosch is telling us the CP8 has proven to be:

• Stronger and more reliable than CP4.2
• Closed-loop lubrication
• Quieter operation

They also added top-feed, dry-service fuel injectors. These are easier to service and work better with the new fuel rail and cylinder head design.

Easier Maintenance All Around

Cummins made sure techs and DIYers would be happy too. The 2025 6.7L is:

• Top-serviceable: Oil and fuel filters are now accessible from above.
• Uses cartridge-style filters that are cleaner to change and more eco-friendly.

Drivetrain Overhaul: New Trans, Transfer Case, and Axles

The engine isn’t the only thing getting love. Ram updated the entire drivetrain to keep up with Cummins’ new output—and to fix a few nagging problems from previous years.

ZF 8-Speed Powerline Transmission

Out with the old, in with the 8-speed. Ram dropped both the 68RFE and Aisin AS69RC transmissions in favor of the ZF 8AP1075 Powerline transmission.

Why the switch?

• The 68RFE was often criticized for inconsistent shifting and limited torque handling, but had tons of aftermarket support. Stock, it was operating on the hairy edge of its limitations, but built Stage 1, 2, or 3 units were able to shoulder really warm 6.7 mills.
• The Aisin AS69RC was strong, but heavy and not particularly smooth, and unfortunately, the aftermarket has been slow to crack the code on what should have been a durable, flexible medium-duty tranny.

The ZF 8-speed is a massive improvement, even if it is “missing” two gears versus GM and Ford’s latest autos:

• Smoother shifting across the powerband
• Better fuel economy from more gear ratios
• Built to handle 1,075 lb-ft without breaking a sweat
• Quicker response for towing, climbing, and daily driving

This isn’t just a transmission change—it makes the truck feel more modern and more confident under load.

Transfer Case: BorgWarner 44-46

For 4x4 models, Ram now includes the BorgWarner 44-46 Electronic Shift-On-The-Fly transfer case:

• 2.64:1 low-range gearing
• Smooth electronic engagement
• Strong integration with traction and stability control systems

This is especially useful for anyone who does frequent trailer work or off-road driving, and it replaces the older manual-shift transfer cases found in base models. With such a deep low range, it’s not necessarily a going to give rock-crawler ratios, but it should easily pull the Ram out of any off road issues drivers find themselves in.

AAM Axles Front and Rear

Ram kept the dependable American Axle Manufacturing (AAM) axles but continued to refine how they’re paired with the new drivetrain.

• Front: AAM 9.25-inch, heavy-duty open or limited-slip
• Rear: AAM 11.5-inch or 12-inch, depending on model and GVWR

Axle Ratios and Options

One of the most important—but often overlooked—choices in your drivetrain is the axle ratio. Ram offers:

• 3.73:1 — Great for balanced highway and towing use
• 4.10:1 — Ideal for max towing, heavy payloads, or steep terrain

Why it matters:

• Lower (numerically higher) ratios like 4.10 offer more torque at the wheels, improving pulling power.
• Higher (numerically lower) ratios like 3.73 give better fuel economy and reduced engine wear.

Some trims (like the Power Wagon) also offer electronic locking differentials, ideal for traction in mud, snow, or sand.

Final Thoughts

The 2025 Cummins 6.7L and the Ram HD drivetrain around it are the result of years of feedback, engineering, and innovation. From solving cold-start issues to ditching the CP4 pump and finally bringing a ZF 8-speed to the heavy-duty game, this is a year worth watching.

If you’re looking to upgrade, maintain, or modify your Cummins-powered Ram, Alligator Performance has the parts, gear, and knowledge you need. Whether you're building a towing rig or a daily driver, these 2025 updates are a solid foundation to build on.

Now, the challenge for any company that specializes in diesel performance, like we do at Alligator, is keeping track of what upgrades and weaknesses in a new model year, or drivetrain, and how mechanics and the aftermarket are supporting these new powerplants. Trust us, it’s a full-time job, but our teams are constantly vetting new products, from cat-back systems to cold air intakes, to tuners to ensure we’re bringing the right options to you at Alligator Performance.