I’m in the SA areaWhere are you in Texas? I see plenty of GM 2500HDs around the 5k-7k in the DFW area in average condition. They are towing/work trucks, so yes, some are well worn. Some are actually nice.
I'm actually blown away that the 1500s of same year and mileage are actually the same or more than the 2500/2500HDs. Every kid in the city wants to drive an ECSB or CC super short bed...Apparently long beds aren't common for mall crawling or doing burnouts on the way to Starbucks. high demand = high prices. My brother just bought a "cheap" 98 RCSB Z71 for like $5k. I bought my K3500 CCLB SRW for $2.5k a few years ago. Mine was a ranch truck in her former years, so a little rough around the edges, LOL. But both trucks have typical problems of their age.
I'm partial to the late GMT400s and GMT800s though. I think they are good trucks.
As for the rear sag, you can add some overload springs or those rubber sumo deals. I don't think they in anyway soft on the 2500+.
6.5's are fine as long as you understand what they're capable of and don't want more. They are what they are, a light duty diesel.I also regularly find the 6.5turbo for cheaper than the gas trucks. Wouldn’t mind one of those, but understand that they have issues and low power.