Well my brother in law has the Flex-A-Lite fan it is has been working just fine. You can hear it a little bit inside the truck but it also has been getting around 22/23 mpg. And stock cfm is 2500. And this fan is putting out around 5000 cfm. So therefore more cooling power and it isn't gonna pull much off your alternator. Just go to there website and look at the amperages. I think it is a good idea. Of course he has other things done to his truck but either way.
for the fan. When you turn the truck off the fan will still run for a min or two. And it sounds like your in a plain on the runway. But not as extreme.