OK Dokey..

Here are the modified physics.

I didn't try it but i think there are some problems with these physics settings:

` chassis.torquePoints = [ { rpm: 0, torque: 200},`

{ rpm: 1000, torque: 100},

{ rpm: 2000, torque: 50},

{ rpm: 3000, torque: 20},

{ rpm: 4000, torque: 0},

{ rpm: 5000, torque: 0},

{ rpm: 6000, torque: 0},

{ rpm: 7000, torque: 0},

{ rpm: 8000, torque: 0},

{ rpm: 9000, torque: 0 } ];

chassis.forwardGears = [ { ratio: 6.20, shiftUp: 10600, shiftDown: -1 },

{ ratio: 4.29, shiftUp: 5600, shiftDown: 5000 },

{ ratio: 3.56, shiftUp: 5600, shiftDown: 6000 },

{ ratio: 2.14, shiftUp: 5600, shiftDown: 3000 },

{ ratio: 1.00, shiftUp: -1, shiftDown: 3000 } ];

You're making the torque decay very fast as the rpm goes up, it's a tractor, and you're setting a very high shiftUp property of the first gear, which it will never reach as it has no torque to go at more than ~ 3500 rpm (unless it's going down a vertical road), so it's always in first gear.

(btw, you can just remove the torque points with 0 torque.)