Will this interfere with the trunk seal or rubberized trim?

No. The air dam is designed to sit cleanly beneath the OEM bumper without contacting weatherstripping or trim panels. Proper fitment depends on correct mounting point alignment and no prior bumper damage.

Does this affect brake light visibility or cutouts?

This lip does not extend into the brake light area. It sits entirely on the front bumper assembly, so no light cutout modifications are needed.

Will this stay stable at highway speeds?

Yes. The one-piece construction and full-width design provide structural rigidity when properly secured to OEM mounting points. Low air pressure under the bumper works with the air dam shape to maintain stability.