i got a 2000 silv. 5.3l. 4x4 and only the 4 speed on the fans switch works. could it be the resistor?

Could very well be. Check for continuity of terminals B and C on the resistor (the terminals that the yellow and purple wire go to. If its open than the speed 3 resistor has burnt out. Since all the lower speeds use the speed three resitor to drop voltage none of the lower speeds will work if it is burnt out. Speed 4 uses a relay that's built into the resistor. The relay has its own power supply for high speed. All of the resistors are bypassed when the switch is set to high speed.