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

These mount at the factory mirror points — no drilling required. They bolt directly where your stock mirrors were, so install is straightforward.

Do the heated mirrors work on a separate switch, or do they tie into the rear defroster?

Wiring configuration is not specified — you'll want to verify harness compatibility with your truck's electrical setup before ordering, or contact support with your VIN for exact wiring details.

Will these towing mirrors remain stable at highway speeds?

Chrome construction and factory-style design are built for stock truck speeds and towing loads. Make sure both glass panels are intact before highway use, and check that power adjustment mechanisms lock securely in position.