What model transmission does a 1999 Chevy 1500 Silverado 5.3L 4X4 Z71 have?

A 1999 Chevy Silverado 1500 5.3L 4x4 Z71 most likely has a 4L60E automatic transmission. However, there's a small chance it could have a manual transmission, though that's much less common for that year, engine, and trim level. To be absolutely certain, you should check the sticker on the driver's side doorjamb or the owner's manual.