Do these mirrors mount to the factory towing mirror holes, or do I need to drill new holes?

These are designed for factory towing mirror mounting points — no additional drilling required. You'll be using the existing holes your truck came equipped with.

How stable are the mirrors at highway speed, especially when extended?

Towing mirrors are engineered for highway stability at full extension. If you notice vibration after install, confirm all mounting fasteners are tight and that the assembly is fully seated against the door.

Will the heated elements drain my battery if I leave the truck parked?

The heating circuit is wired through the ignition — mirrors only heat when the engine is running. No parasitic drain when the truck is off.