If the truck is in good shape and the miles are the only concern I would say that is a great deal. I paid nearly 6k for my 2000 model extended cab 1500 series with the 5.3l engine and I'm very happy with it. It has almost 140k on it and everything works great. I have a friend that recently sold his and it was still running strong with nearly 250k on it. He got the truck in high school and ran the Hell out of it all the time and it never gave him any major problems as far as I know. One thing that is reassuring to me is that the engines are cheap and easy to find if something major did go wrong with it. It is a truck with a v8 so I wouldn't expect the fuel mileage to be great. I know its worse than my 6 speed Camaro when it was stock.
I bought a 2001 Silverado Ext cab Z-71 last october. So far here is what I had issues with:
-ABS module was DOA, easy fix and it only cost $150 to have it rebuilt with 5yr warranty
-Groan when taking off from light, slip joint on the drive shaft needed lubrication
-water in headlight lenses
-speedo needle jumps, bad IP motor and easy fix
That was about it other than a slight oil leak. With the stock size 265/75/16 tires and being easy I get about 15 city and 18 highway with it. Will know soon how it does with the new tires 285/70/17 I just put on it.
Better figure in a tune up (plugs, fuel filter, air filter, and anything else you can touch) as I doubt anyone else touched it yet.
My step brother has almost 300,000 miles on his with no major issues, my dads 1996 yukon has over 400,000 miles with no issues. They are a solid platform as long as you put some time and money into them.