00-02 is what I personally prefer. They're electronically a bit simpler. Engine, transmission, axles, brakes are the same 00-06.
If electric fans are a concern, that's an easy retrofit. I put electric fans on every vehicle I own to replace the mechanical fans.
All that said, 02-06 are still great trucks and I would (and have) owned them.
The biggest thing is finding one that's been well cared for. If you can get service history with it that's a major bonus. In those year models, the transmissions are all 4l60e's. I've seen them go out at 100k miles, I've seen them last 250k+ miles. I replaced the '60e in my Tahoe at 280k miles. It all depends on how the truck was driven and cared for. Mine was daily driven the first 17 years of it's life, mostly highway miles, by the guy that bought it new. Around 200k is fairly typical if it's not been abused but it has been used to tow some.
Engines can last a long time. Long long time. There are some running around with 400k+ miles on them. My personal just clicked over 300k and still makes 65psi of oil pressure running down the road. Very happy motor long as I let it warm up for a minute or so.
If you can find one that has hydrostatic brakes, that is a killer system. My old Z71 Tahoe had them and my current 2500 work truck has them. I intend to retrofit my current Tahoe as well.
There's not a lot of bad in these trucks. The biggest thing is finding one without much rust. You may decide to find one that the trans is already going out in at a really good price and have a *reputable* transmission shop rebuild one for you, if you have one around. I'd be willing to travel to find a really good trans shop. Ask local race shops where they recommend rebuilding 4l60e's if you decide to go that route. Alternatively you can order a trans from a big name rebuilder (Gearstar for example) and have a regular garage install it.
A big indicator of trans health is the color of the trans fluid. If it's brown it's been hot. If it's bright bright red it's recently changed. If it's mostly red it's probably old but the trans has probably not been abused. Wipe it on a white paper towel off the dipstick to look at it. If it has fresh new trans fluid in it and it still drives well, that does at least tell you that there's still material on all the clutches. If a '60e is badly worn and you replace the trans fluid then it will sometimes never move again. The old clutch material suspended in the fluid is sometimes all that's keeping a badly worn trans moving.
That's about all I've got. Ask if you've got questions. The trans is the only real weak point of these year models, but the '60e is still a good trans. I've built several of them and I use them well above their original intent, so don't be afraid of them. Just look for the warning signs. Most of these trucks are high mileage now.
