When the clutch on the fan engages, then the engine is actually working the fan at power/force. The old off set metal fans really sucked the power out of it. The current light weight fans are considerably better.
Get on Amazon.com, go to the automotive section. search accessories and you'll find what you are looking for from different manufacturers. It will even make sure it fits your truck before you attempt to order it.
I live in Texas, where it gets HOT! Honestly, I haven't really noticed when the fan clutch engages, but then again, the A/C is blasting pretty loud. I'm not sure if it would help to much with gas mileage.