The 2019 Ram 3500 now gets 400 horsepower and 1,000 pounds-feet of torque from its Cummins high-output diesel, but what does that mean for fuel economy? We took a Ram 3500 Limited 4×4 crew-cab long-bed dual-rear-wheel pickup truck for two fuel economy runs to find out.

Related: 2019 Ram 2500/3500 First Drive: Going for the Beef

The Cummins engine remains at 6.7 liters of displacement and uses the same design and layout as before. However, there have been many improvements. The block is now made of compacted graphite iron to save weight (60 pounds) while retaining strength, and there’s a new cylinder head design, new valves, springs, rocker arms, pistons, rods, bearings, exhaust manifold and updated turbo. To accommodate the higher power output and load ratings, Ram upgraded the transmission, frame, suspension, brakes, axles and transfer case.

MPG Route and Setup

Our Utah test route covered steep grades, freeways, highways, city streets and low-speed curvy mountain roads. Elevation ranged from 4,500 feet to 5,400 feet with some steep sections and some relatively flat ones. The total distance was 62.3 miles, according to Google Maps, and the truck registered a surprisingly close 62.1 miles for both trips.

We ran the loop twice: first with the truck empty except for the driver and the second loop with a PJ equipment trailer loaded to 16,000 pounds with a 1,600-pound tongue weight and attached to the truck using a weight-distribution hitch. The trailer was loaded heavy and low, thus not presenting much wind resistance, which is a major factor for fuel economy, especially at speed. This load range requires the driver to have a commercial driver’s license, and I have one.

For both runs, the air conditioning was set to max, the transmission was set to Drive, the rear air suspension was in the default position and everything else was left alone. When towing, the same was applied, but Tow/Haul mode was turned on and the exhaust brake was set to auto. There was no manual shifting and no idling beyond sitting at red lights.

Our Ram 3500 was equipped with the transfer case skid plate, a tonneau cover and the Max Tow Package that includes the 4.10 axle ratio, rear air suspension, Department of Transportation safety kit, Fifth Wheel/Gooseneck Towing Prep Group with a fifth wheel hitch and a few other items. Of course, the $11,795 high-output Cummins diesel engine was added on to get maximum tow ratings. Inside, it was equipped with the 17-speaker sound system, 12-inch display and surround view camera system, among other things. The total price including the destination charge was $87,810.

According to the tire and loading information sticker on the doorjamb, the truck’s payload capacity was 4,818 pounds, which put the towing capacity at 30,800 pounds with a 15 percent tongue weight and 185-pound driver. The total gross combined weight rating came in at 25,182 pounds. We also put in the vehicle identification number on Ram’s website and it showed a max payload of 5,320 pounds and towing capacity of 32,360 pounds. Given all the added options and extras, we believe that the door sticker is probably the right number.

Ram 3500 High-Output Diesel MPG Results

Empty of everything but the driver, DOT safety kit and fifth wheel hitch, the Ram 3500 ran the route netting 13.8 calculated mpg using 4.52 gallons of fuel; the truck’s onboard trip computer read 15.1 mpg. When loaded with the 16,000-pound trailer, it averaged 9.5 calculated mpg using 6.58 gallons of fuel. This time, the truck’s computer read 9.9 mpg, which was much closer than the empty run, but still off.

We were surprised to see the low unladen fuel mileage, even with the equipped 4.10 axle ratio. During our 2018 One-Ton Heavy-Duty Truck Challenge, the single-rear-wheel Ram 3500 with the 3.42 axle ratio returned 16.9 mpg empty and 9.9 mpg when towing; granted, that different test is not directly comparable, but it did have similar laden results.

Each of the two runs took about an hour and a half, with the loaded run taking an extra eight minutes. We didn’t notice any traffic that would have affected the fuel mileage runs, which means the extra time in the loaded run was due to exercising more caution with the heavy load.

There is one reason to buy this truck, and that is to haul and tow anything and everything. With poor fuel economy when empty and comparable to its class when heavily loaded, this truck is meant to be used as a workhorse. Having the extra wheels in the back makes city driving and parking difficult and even annoying. On the flip side, it remains stable and composed while hauling very heavy loads and never feels short on power. Of course, it does all this with an excellent ride and comfortable high-end interior.