[MooseSuite]

Fantastic Vent Is a good product. Not knowing what you are comparing, year model etc I can't think of anything further. You can check the volts going to the fan motor , but both fans not operating to your expectation. If in warranty Fantastic Fan will replace, they will also trouble shoot your issue over the phone. I'm not sure if you have done this.
I assume you have checked your battery load output.