Most likely the resistor. I replaced it in my 01 quad slt this summer. It is under the glove box. Look for a wire harness connected to the resistor that sticks straight up into the blower ducts. There are two screws holding the resistor in the ducts. I also took one screw loose on part of the duct below to give me a better angle on the other two screws. The part only cost around $12 from the dealer. There is a red clip on the wire harness that needs to be removed before you can remove the wire harness. Good Luck!
I have read many posts in the past year that claim the reason for the resistor block burn up was a defective blower. I have just had my resistors replaced at the suggestion of my mechanic, with this info. The blower works now, but will be on the lookout for it to quit again. I have 2 years warranty on the repair, which is the only reason I let him change them.
The thought of an other mans hands on my truck.. eeeew.
just fixed this one , if all you have is high you wont have it long. Its a switch,works like a dimmer sort of, replace it .Its behind the knob cheap part
so an easy fix if you are able still not bad if the mechanic does it.