According to the IGN Wiki, the following upgrades have an effect on the car's performance: Armour (+20-100% defence). Brakes (increase breaking). Engine (increases acceleration).
The Imponte Duke O'Death is a two-door armored muscle car featured in the enhanced version of Grand Theft Auto V, and released in Grand Theft Auto Online as part of the continuation of the Cunning Stunts: Special Vehicle Circuit update. It is stored as a personal vehicle in GTA Online.