I have a 2003 ford explorer and if I drive it cold it will rev up higher than normal and move slow and it will be stuck like that for a couple of days then go back to normal if I let it warm up before taking off..what could this be?
Is this a 4x4 model? If so could be a problem with the transfer case or you could be switching into LOW accidentally.
If you're capable, do a full diagnostic. It sounds like you may have more than one problem.
If you're not a real wrench monkey, take it back to the shop. If you're talking about the radiator fan, that could result in over heating and thus loss of power, but it wouldn't be intermittent.
Most problems with the power plant don't really come and go like that. That's usually what you find in something computer controlled like intake, injection and the transmission. Id honestly recommend taking your vehicle to another shop and having them check if the work you were billed was actually done correctly. If the shop messed up something that could easily cause this issue. But again, it would be a transmission related problem.