My experience is not in a GM HD, but for what it's worth:
Gas 3/4 ton--Handled typical loads (boat, car on trailer, tractor on trailer, etc.) well IF you didn't mind it revving to the moon on hills or pulling out in traffic. Bad fuel mileage empty or loaded. Ride was firm, but not uncomfortably so. Felt like a truck.
Diesel 3/4 ton: Basically does not care what you put in or behind it. There's nothing like pulling a hill in the left lane, in top gear, passing slower traffic with 10K pounds (obviously less in the case of the boat) on a trailer in tow. Fuel mileage on a 55 mph country two lane 35 mile trip (you described my commute to within 5 miles) is excellent. Loaded mileage is 3-4mpg better than the gas equivalent. Ride was the same, if not a bit better than the gas truck (heavier diesel motor).
The diesel takes about 8-10 minutes to get up to temperature on my commute.
Cost of diesel in proportion to gas sucks nowadays, but if you're a "car guy", the diesel will make you smile. Higher resale is the icing on the cake, although that's not a factor if you're leasing.
Last edited by soacj; 11-14-2013 at 10:40 PM.