Do these mount at the factory mirror location?

Yes, these bolt to the existing factory mounting points — no drilling or bracket fabrication needed. Swap the originals for these and you're done.

Will the mirrors stay stable at highway speed when extended?

Factory mounting and construction are designed for towing loads and highway conditions. If you're running wider than stock, test positioning before committing to regular highway use.

What wiring is needed for the power and heat functions?

Exact wiring diagram and connector type are not specified — consult your truck's factory service manual or wiring harness supplier to confirm compatibility before installation.