Back in 1993 I owned a new GMC 1/2 ton with a 350 engine. It was my first truck and the dealer told me I could pull any camper I wanted. Our first camper was a used 1988 24 ft Mallard travel trailer. It pulled heavy and I put in a transmission temperature gauge. It was running to hot, so the dealer put in an aftermarket transmission cooler. It still pulled heavy so we traded for a fifth wheel that was new and lighter even though it was a 26 foot. We kept that a year and traded for the lightest 5th wheel I could find. It was 23 feet and the weight with everything on it was 4700 lb. We did ok with that. I think my engine was a dog. One day coming back from Minnesota we were just west of fargo headed west. Wind was 15 mph from the NW and I tried to pass a semi that was doing 65. The wind coming off his front would stop me. So I got behind and pushed it to 75 and started to pass. I was able to make it to just about his front bumper and again it stopped me.
I can't remember when the Duramax came out if it was 2000 or 2001, but we bought a new 2001. Within a year we bought a 29.5 ft 5th wheel. In 2012 we bought a new Duramax and in 2014 a 37 ft 5th wheel. Loaded it's 17,000 and with the boat behind it pulls easily. As long as I own a camper I'm sticking with diesel. With the smallest camper we had and the old gas truck I and a son headed to the badlands for turkey with a 40 mph headwind. Top end was 55 mph and my mileage was just under 5 mpg. Didn't know a truck could suck that much gas.
With the old 350 gas engine I was limited to under 5000 lbs. My brother-in-law had the identical truck and pulled a six horse trailer with horses. Maybe I just had a dog.
Edit: When the newest (2014) camper was two days old we headed to Texas for the month of January. Everyone kept flashing their lights at me at night. I wondered what was with people. I could pull without adding suspension, but I noticed my back end really dropped when I hitched up. Evidently my lights were in everyones eyes.