The mileage while towing will probably be similar to what the 1500 got towing but for day-to-day driving you will notice a big difference. The tank on the 2500 is also much larger so expect the price at the pump to be a good bit more. I went from an '18 1/2 ton Sierra to 1 '20 2500HD Crew and then a '21 2500HD. I enjoy driving the larger truck more so I put up with the cost of the extra gas.