Proper lube level for a Mag-Hytec cover

I agree with using the higher fill level. Remember that the aftermarket cover is deeper, so that adding more fluid doesn't raise the level of the fluid as much as it would with the stock cover. OEMs get by with the minimum level of lube that will do the job under an average duty cycle which includes some towing. If towing at the limits and for long periods, it makes sense to add more fluid and keep it cooler.

Not all aftermarket stuff is snake oil...these parts are available to help us adapt a general purpose truck from the mfr into one that is purpose-built for how we use it.