ORIGINAL: jcbst12

The only real difference between the years:

1. 99-02 Silverados 270-275 horsepower. 16-20 mpg on average. A little easier to fix and a little less costly if you find one with low miles.
2. 03 and up have electric fans and a little more horsepower than 99-02. They are also are E85 compatable.
3. I believe 05 and up use drum brakes instead of disk brakes in the rear which are easier to work on and last longer.

The 1999 5.3 had 265 hp.
2000-2003 has 285.
2004+ had 295
and I think in 05+ there was an aluminum 310 hp version avalible.

99-04 had DISC/DISC... 05+ has disc/drum. If you live up in the "salt states", the disc/drum is the better option.