Will these mount at the factory rocker points, or do I need to drill?

These use factory mounting points — no drilling required. Your existing mirror holes line up directly.

Do the heated elements work independently, or do I need to wire them to a switch?

Heating element wiring is not specified — consult your F-150 service manual or a qualified installer for proper integration with your truck's electrical system.

How stable are these at highway speed when fully extended?

OE-style design means the same structural rigidity as Ford's originals. Full extension is safe for towing and highway use; just tuck them in when you're not towing to reduce wind noise.