Thats what I was getting at, those Banks graphs are marginally helpfull and don't give you real world SOP feelings of the engines in question.
I wouldn't worry much about if it has a hitch or not. If the truck is in good shape, then that is what counts, not really if it has a goose ball in the bed or not. My '01 has a goose hitch and is pulling a trailer 50% of it's miles, but it's the cleanest 2nd gen you'll find and is ready for a trip across the country on a moments notice. Pay close attention to clues on how the owner has taken care of the truck, that would be my #1 tool looking at these trucks.
My '01 had appeared to never have even seen a trailer behind before I bought it. Just by looking at the trailer plug and the inside of the hitch I could see little to no wear. My dad's '02 on the other hand had a goose ball and an exhaust brake, truck also came from Colorado. It probably got it's butt worked off. My '01 hasn't been anymore problem free than my dad's truck and when pulling a lot, his even seems to burn just a hair less oil. I believe it's the way these engines get broken in. If you drive them easy and never load them up at all, they are going to wear in under those conditions. If you let the rings break in, and then put that engine to work, they seem to become more accustome to being used to full capacity and don't use as much oil when they get older. I'm not saying this is the case in every situation, but just something I've found as a trend in different new and used equipment I've owned over the years.