2002 GMC Envoy fan blade running extremely fast

Monday my Envoy started making a strange sound. It sounded like a jet plane taking off. When stepping on the gas the car would not excelerate like it should the rpm's were around 2.5 to 3 and the car was only going about 35 to 40. I checked the transmission fluid and valve which it needed a quart of fluid and we put cleaner on the vavle because it was a little sticky. This did not work. We thought then that it might be the fan clutch because when the belt and fan are off the car it idles and sounds normal. My question is what else could it be? The fan clutch seems to be ok.