The Tempest line was changed to an intermediate-sized car on the new GM A platform in 1964. The LeMans returned to its role of Tempest trim upgrade, which included carpeted lower door panels, deluxe steering wheels, courtesy lighting, and full wheel covers. For 1964, a two-door hardtop was added. A new 215 cu in (3.5 L) I6 was introduced, as well as a redesigned 326 cu in (5.3 L) V8 that now actually displaced 326 CID.
Shortly after the start of the 1964 model year, the LeMans became available with a new performance package designated as the GTO, or 'Gran Turismo Omologato'. The GTO option included a 389 cu in (6.4 L) V8 from the full-sized Pontiac line that produced 325 HP with a four-barrel carburetor or 348 HP in Tri-Power] version featuring three two-barrels.