the 3.4 L V6 was dropped as an option for the regular cab models, which were available only with a 2.4-L or a 2.7-L four-cylinder engine. An aftermarket Toyota Racing Development (TRD) supercharger kit was available for the 3.4-L V6, raising output to and . The V6 supercharger kit was specified for model years 1997 and later, as the earlier engine control units (ECUs) had limitations. A kit to add a 7th fuel injector was available, including a replacement ECU, boosting performance further to and . In addition, TRD supercharger kits were available for the 4-cylinder engines (2.4 L and 2.7 L) as well. A five-speed manual transmission was standard for all models initially, with a four-speed automatic transmission available as an option except for the 4WD V6 regular cab. The PreRunner (MY98–04) and Double Cab (01–04) models were available only with an automatic transmission for the first generation. The 3.4 L V6 was paired with the R150F manual transmission or the A340F (4WD) or A340E (2WD) Aisin automatic transmission; the A340F code is 30-40LE. The first-generation Tacoma has a fully-boxed frame (meaning the main frame rails have a closed rectangular cross-section) until immediately after the rear leaf spring mounting bracket, where the frame transitions into a C-shaped cross-section. The TRD Off-Road package was introduced in 1998. This package added a locking rear differential and was only available to PreRunner and four-wheel drive models that were equipped with the 3.4-L V6. Antilock brakes were made standard across the Tacoma line for the 2003 model year. Updates The first-generation Tacoma underwent its first minor update in October 1996, switching from recessed sealed beam headlamps to a flush design on 2WD models. There were two more cosmetic facelifts: the first in July 1997 and the second in October 2000. The most visible changes were in the modified front grilles (both facelifts, for model years 1998 and 2001) and tailgate badging and emblems (first facelift, MY1998). The MY1998 facelift included distinct grilles for the 2WD and 4WD models; 2WD models featured a prominent horizontal bar splitting the grille. A StepSide bed was added as an option for MY2000. Mechanical changes included a switch to distributorless ignitions (coil-on-plug) in 1996 and in 1997 longer rear leaf springs. A passenger-side air bag was added in July 1997, and the driver's-side air bag (standard from 1995 launch) was "depowered". Most 4×4 models came with Toyota's Automatic