Have had this 2003 Z71 2-dr since new. It currently has 134,000 miles. No complaints about reliability with just basic maintenance. Original tires only lasted about 40,000 miles. Replacements have lasted about 80,000 so far. Only parts that have broken on me are two rear U-joints,water pump seal seeps, and the battery died after 7 years. Clunking noise from steering column is a little annoying, but apparently common for this model. Under-body rust is a problem even though I regularly wash the underside of the truck. 4x4 system has been rock solid in snow, ice, mud, you name it. Tows/hauls with no problems although trailer brakes highly recommended for heavy loads/high speeds.
I'm a contractor in Northern Vermont and this is my work truck. Cost 21k new w/ auto 4wd and air. 185,000 miles of merciless beating and still running hard. Work cap full of tools and ladders weigh enough to need helper springs just to get it to ride normal, and I keep this kind of weight in it 24/7. I regularly tow my dual axle dump trailer full of construction debris, and the 4.8 liter does fine. The thing eats brakes, but Chevy does make a 3/4 ton. The paint is peeling a little where there are dents or scrapes, but no real rust-the galvanize is holding up well. The steering clunk was fixed under warranty and I've spent about $3k on repairs and maintenance
I have had my truck for about 55,000 miles. I purchased it certified used about 3 yrs ago. I am about to turn 100,000 miles and the only problems I have had with it is a dead battery and a broken power window motor. The truck runs well and is ultra reliable. I wish the fuel economy was better (I think I get around 14 mpg). I feel like I will get another 100,000 miles out of it before it needs to be replaced. "American" car companies build trucks well...its what they do best in my opinion. I wouldn't hesitate to buy another Chevy or GM truck again, but I would aim for an extended cab for the extra room and convenience. Overall, I have been very happy with my purchase & recommend it.
I have over 110,000 miles on my p/u and have had only one part break ($25 U-joint + 1 hour of my time to replace). I'd say that's great reliability! Still runs close to as strong as when I bought it and can pull a loaded trailer (roughly 5,000 lbs) with no problems.