Will these maintain stability at highway speeds with a full trailer load?

Yes — these are engineered for the rigors of towing. The extended design stays rigid under crosswind and trailer sway. Make sure they're bolted down tight at factory points for full stability.

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

They mount at factory points — no drilling. Line them up with existing holes and you're good to go.

Will the extended mirror heads interfere with the truck bed when I turn tight?

Test-fit after installation to confirm clearance on your specific truck. Mirror reach varies by build, so a quick parking lot check prevents surprises on the road.