1-2 fan position not working.
#2
Same Problem
Had same problem on my 99 silverado. I had to buy a part that was located near the inside filter kit at the passenger floor board. I changed that and now mine works on all settings. Part came from auto zone an was about a 20 minute fix.
#6
Could be. The ones I have seen are wire wound resistors and each position (fan speed) has a resistor or a combination of two. As was said earlier, the fan speeds that are used the most are the first ones to burn out. If a combination of resistors are used, one resistor could take out two speeds.
#8
Don't the 2004's have the electronic display with a bunch of lines instead of 1,2,3,4 like the older trucks? I know my wife's 2003 Tahoe has all the lines so there are a lot more than just 4 speeds.