IIRC gas models have same oil change schedule as the diesel.
Jeep Grand Cherokee WK2 - Maintenance information and schedules
The Diesel is a wash on most issues. If you buy DEF from the dealer they want $30-$40 for the 2.5 gallon - get it from the auto parts store for cheap just make sure it meets the specs and has a recent production number. Only add 2.5 gallons at a time and don't fill up tank unless you live in cold climate as it's perishable (especially if you live in hot climates and park it for long time outside in the sun where it can go bad very quickly).
Oil changes cost more but I put synthetic in my gas and diesel vehicles. Spark plugs are cheap so not much of a cost to most people who can afford these trucks.
Fuel mileage is where the diesel really makes a big difference. I can get 800 miles to a tank highway and my bladder cannot hold out that long (it's amazing to see 34-36 mpg highway when keeping it under 70 mph). Compared to my friend with the v6 (low 20's combined) and v8 non-srt8 (mid teens combined) within the same living area and traffic the diesel get's mid 20's combined. The way I see it as I get the torque of a big v8 and fuel economy of a 4 cylinder Cute Ute. Towing it's even more of a slaughter for the diesel as it will destroy any gas truck or suv towing the same trailer. Hell I get 20 mpg highway towing a 14x7 enclosed 5,500 trailer if I keep it at 65 mph or slower. Even crawling along on 2 lane roads and going 45-55 mph I've seen 40+ mpg over long stretches with little need to slow or stop.