Does this mirror use factory mounting holes?

Yes, these mount at the factory attachment points with no drilling or modification required. Bolt straight in.

Will the mirror stay stable at highway speeds when extended?

The power motor locks the mirror position once you release the adjustment switch. Stability at speed depends on how tight you secure it to the mounting points—follow your truck's service manual for torque specs on fasteners.

What wiring does this need?

You'll need to run power and ground to the mirror for the heating element and adjustment motor. Exact wire gauge and fuse sizing aren't specified—consult your F-150 wiring schematic or have it installed by someone familiar with your truck's electrical system.