I've had dual efans since the life of the truck (60K miles) and the only thing I've ever had to fix was one of the controllers.

For whatever reason though when the second fan comes on (hi temp or turning on the A/C) I can almost always feel it kick on through the gas pedal. You can feel it more noticeably at higher rpm's like during highway driving so it becomes kind of annoying, almost like a little surge I can feel in my foot every 5-10 min. Over the years I've installed a Mean Green HO alternator, had a Optima Red Top and now a Optima Yellow top battery with no real luck.

Granted I have a ton of professionally installed audio equipment but when the second fan kicks on there's no drop in rpm's, lights dimming, or anything to indicate a wiring issues somewhere. Both fans are calibrated for a low/hi temp specs and there's no over heating issues.

Any ideas on how to troubleshoot this? Not sure what else I can do honestly.