As I recall they are not the greatest you could use. Others here are using Tauras fans (dual fans). These trucks move a LOT of AIR with the engine driven fans. I don't think you will do better with an electrical fan. Others here will argue this point.
Honestly, I am a proponent of electric fans but on the SD trucks that have inter-coolers they arent as effective, especially for towing. And if you do stop and go driving in town traffic they really arent suited for the purpose. Other than that, I think electrics are a good choice.
thinking out side the box, besides cyclone, has anyone tried a set up that is similiar to the 6.0's, it might as well be electric. even when at idle when it engages, it picks up small rodents, and at high idle it creates it own mini tornado
that way you got a strong engine driven fan to pull air and it completly disengages when not needed.
I tried the pure electric fan idea a few years ago and at that time couldn't get that would keep her coolunder a hard pull. On this truck I just wanted to shore up the factory fan for heavy traffic and warm weather. Don't laugh but the fan I found in the shop is from an Old's V6 diesel. Its 14' and two speeds. Low speed seems to do the trick. You can tell because the A/C works in traffic just like at 60mph. High speed will suck your shirt into the grille. Plus when you shut her down the fan can continue pushing air through. To bad in doesn't run the water pump too.