In 1979, a new model Terra-Gator 1603 came to replace the old Terra-Gator 1253. Three-wheel design has several advantages. It prevents soil compaction and provides excellent maneuverability (front wheel has a 90-degree rotation angle). The new model looked almost the same as its predecessor, but it was equipped with a Caterpillar 3208 or Cummins V/VT555 engine and 10-speed manual transmission Fuller. There was also a Terra-Gator 1603T model, equipped with the same engine, but with turbocharger.
The updated family also included Terra-Gator 1703 and Terra-Gator 1803 with Cummins 6CTA 275 hp or John Deere 6081 (only Terra-Gator 1803 model) engine and 18-speed Eaton manual transmission or an automatic Allison. In 1991 the most powerful version Terra-Gator 1903 has been added to the range. It was equipped with a Cummins L10 (350 hp) or Caterpillar 3176 (400 hp) engine and a mechanical 18-speed Eaton transmission. Tires on all versions have dimensions of 66×43.00-25.