RE: 1998 Silverado fan speed problems. . .
Both of your problems are simple. The fan speed problem is the fan reostat or resistor depending on who your talking to. Its located under the right side of the dash right beside the fan. It should have a four or five wire plug in on it and two or three screws that hold it in the heater box. The outer piece of the dash surround just clips on, just pull back on the corners and it will come loose, you will have to have the key on partially to drop the shifter down to get the surround passed it. And the radio just clips in also, push the clips down and it will slide right out. Its self explainatory once you have the surround off. Good luck.