Will the diffuser scrape on steep driveway angles or speed bumps?

The diffuser mounts to the factory bumper's lower mounting points and follows the OEM rear fascia profile. If your vehicle clears the factory bumper on inclines, the diffuser will too. Check clearance by confirming your current suspension ride height before installation.

Does this piece provide functional downforce or is it purely cosmetic?

AM Design's diffuser is styled for visual continuity with the rear bumper. Aerodynamic benefit is minimal at street speeds; the primary value is extending the aggressive lower-rear line. For measurable downforce, a full splitter or wing system would be needed.

What prep work is required before painting?

Sand and prep the surface according to your chosen paint system's guidelines. Since the piece Requires Surface Prep, verify the entire surface is clean and free of dust before applying basecoat and clear. Your paint supplier can recommend grit and primer specifics based on your coating choice.