I know what is wrong with your blower, the same thing happened to me and it was an easy fix. Go to your chevrolet dealer and ask them about a resistor for the blower motor. I had it fixed and it was pretty cheap, like 20 bucks. If you want me to, i can pull the reciept from it and possiblely get you a part number for it....
my email is
[email protected]
let me know,
mike