An abbreviation referring to the Mitsubishi 3000 GT, a once-popular sports car that is no longer manufactured.
Mitsubishi also made a higher performance model, the 3000 GT VR-4, featuring ~300hp and the unique capability of all-wheel drive.
Though these were sweet, beatiful machines, were quieter, with a better ride, and had the means to move quick; they were slightly overweight, a bit underpowered, and front-wheel drive - making them inferior to other cars in their class (the camaro, firebird, and mustang), in terms of racing.
"Yeah, I was on one of the 3kgt fan sites looking for some performance mods."
Person A: "I need a ride to my friends to pick up my mitsu."
Person B: "Your mitsu? What kind ya got?"
Person A: "got a 3kgt"
Person B: "Ah."