I have gremlins in my 2000 Denali again. The blower only blew on high yesterday. Blower motor resistor right? No, I replaced the part and no change. It blew on high with everything disconnected on the way to Autozone. So I said fine I’ll just disconnect the plug again to get high fan again, but no luck. I swapped out fuses and stilll no change. What could it be??