If any of the 96-99 GMT400s still have the spider injection setup, people had issues with those. Otherwise, it's as solid as anything else. Those things are everywhere for a reason, I'd argue. I wouldn't run out and buy one probably ever unless it was free or I was in a bind for a pickup and the price was at rock bottom, but if I was, I'd go with an 88-95 because that's TBI, and I know those pretty well. Plus, it's pre-SRS. Stupid government. The passenger car impact bumpers from the 70s and 80s don't upset me, but airbags are annoying to me. I know Gen I and III Vortec some, but you can't diagnose those like a TBI or CCC car or truck. What I mean by that, is TBI literature is everywhere, and it's very simple to work on. When it's free of bugs, it's super reliable. You need to have a decent OBDII scan tool for earlier stuff, probably around 96-02/03. I don't mean dealership level or anything, but an aftermarket tool that can get in there a little bit and give you some good info instead of just telling you Code P0740 and goodnight. On a TBI, it's a paperclip that you swiped from somewhere earlier or a four dollar homemade Chinese scan tool and some public domain software if you really want a top of the line setup.
I have some experience with my mom's '02 Suburban 1500 with a 5.3. That has been an excellent vehicle. It's starting to show its age now with needing more complex maintenance more frequently, but even then it's still good, and all vehicles do that. It's probably got around 225,000 miles on it. I like the traditional stuff so no the no distributor, coil-near-plug setup bothers me. The drive by wire also doesn't agree with me. The heater core, condenser, and blower being hidden under the dash gets on my nerves. I know the heater core is hidden in a square, but that's one thing, and my daily has it under the hood, not in the dash, which made changing it a breeze. They're good vehicles, but GM started going in the wrong direction with their stuff in 1996 trying to make it more and more complicated (in my opinion), and they arrived there some time ago for me, but that being said, I don't think it was immediate. I could rant all day, but I'll never buy a newer vehicle because I'm completely in control of what I need to get done with my older current and desired vehicles. It's a personal preference, though. You should be just fine with an earlier GMT800. It'll get you there and back completely reliably. The desirability of Gen III motors for swaps speaks for itself.
I don't know if I'd get the round style Ram. What about a 86-96(97) Ford? Those guys are everywhere, and my dad was in love with his '96 F350 7.3. Honestly, I like the square body design so until '91. I'm ambivalent on the GMT400 so I'll say no preference for or against. Ford held onto their good looks until 1997 if it was bigger than a half ton. '96 if not. And Dodge kept theirs until 1993. I know everyone says they used it for too long, and I agree, but it's still a good looking style. After these, I pretty much tune out with respect to my preferences. They all did a round style of normal proportions, and then they all got huge after those respective styles ended.