Will this interfere with the factory bumper seal?

No. The lip mounts to the existing bumper attachment points and sits below the seal line. Once installed and finished, it blends cleanly with your bumper without compression issues.

Can I use adhesive, or do I need to drill?

This lip is designed to use factory mounting points, so you won't need to drill into the bumper. Fastening method depends on your vehicle's mounting hardware — verify your OEM bumper attachment style before assembly.

Is this stable at highway speeds?

Yes. The low-profile design and rigid FRP construction keep the lip planted without creating lift or vibration. Ensure fasteners are tight and check them after your first few drives.