Help 99 Tahoe a/c heater blower problem

[CaribbeanHigh]

The a/c blower on my 99 Tahoe quit working on low and medium speeds but would workfine on high. Next it was intermittent on high and now it doesn't blow at all. I suspect it is a relay but I can't find the a/c heater blower relay. I checked the fuse / relay box in the engine compartment there is a a/c relay (which I suspect is for the compressor) and there is a blower fuse both of which are fine. Is there another relay somewhere? If so where the hell is it? I have also read elsewhere here it might be a resistor Where would that be located and how difficult is that to replace? I really need to fix this quick it is supposed to be 100 + tomorrow

Thanks for the help