Differences Between the GMC Sierra Heavy Duty Pickup’s Two 6.6-liter V8s

You have many choices to make when it comes to your 2025 GMC Sierra Heavy Duty pickup truck. In addition to cab and bed choice, trim level, and optional equipment, another major decision must be made. Do you want to fill it up with gasoline or diesel fuel? For some, it’s not an easy choice, especially when both engines happen to be hard-working 6.6-liter V8s.  

SlashGear recently talked about the differences between these two engines that are available for your 2025 GMC Sierra Heavy Duty pickup truck. The editors began by explaining that “traditionally, diesel powerplants have proven that their extra torque is usually the more capable and preferred option for heavy duty hauling. The question then becomes whether these improved, more powerful gasoline V8s are capable of doing enough to win over diesel-buyers.”  

What’s the real difference between the two engines? The gasoline engine is a naturally aspirated 6.6-liter V8 rated at 401 horsepower and 464 pound-feet of torque. The diesel engine is the turbocharged 6.6-liter Duramax V8 rated at 470 horsepower and 975 pound-feet of torque.   

Power numbers translate into capability. For example, the gasoline V8 can haul up to 6,820 pounds of payload with a maximum tow rating of up to 18,800 pounds using a conventional hitch (18,650 pounds through a fifth wheel/gooseneck connection). These numbers are for a Sierra 3500HD.  

On the other hand, the Duramax diesel has a maximum payload rating of up to 7,290 pounds. Maximum tow ratings go up to 20,000 pounds with a conventional connection and 36,000 pounds using a fifth wheel/gooseneck connection.   

SlashGear brought up the point about running costs. Yes, 87-octane gasoline is generally less per gallon than diesel fuel. Plus, diesel engines require the extra cost of adding Diesel Exhaust Fluid when it is necessary.  

Considering everything, SlashGear stated that “whether you opt for the gasoline V8, or the upgrade to the Duramax, you’ll get to appreciate a lot of the improvements GM has put into these engines in recent years. It’s really just a matter of how much torque you need, and how often you need it for heavy-duty towing.”  

It comes down to a matter of choice based on your preferences and how you will use the truck. These two engines that power the 2025 GMC Sierra 2500HD and 3500HD are built for the long run. To see which engine works for you, contact us at Ewing GMC of Plano to give the 2025 GMC Sierra Heavy Duty pickup trucks a look—in either gasoline or diesel.