Here's a mpg test of a 2019 with the 1000 lb-ft engine towing 16k vs. unloaded.
CLICKY"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.
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.
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."
