Check out Steve Brotherton's comments in the following thread about testing a fan clutch.
checking 603 viscous fan drive
I think there's more to it than just seeing it spin freely once the engines warm. I changed mine out for this reason and saw no reduction in temp.
You mentioned early on about cleaning the radiator...bugs, etc. In my opinion, the only way to do this is pull the radiator and flush both sides once out. This will also allow you to do the same to the A/C condensor and in order to really do it, you'll want to pull the aux fans off so you have a clear shot at the whole front surface of the A/C condensor. While the radiator is out, you way wish to have a shop clean it professionally - inside and out.
If you're seeing higher temps on the highway, you could indeed have a blocked air path.
If it's running hotter only at slower speeds, it could be the fan clutch or a blocked air path, or ?????????.