These are my thoughtson information gathered from the Internet on the use of tuning chip boxes. The engine settings have safety parameters for poor quality fuel and air quality etc. in third world countries,now Chevrolet wants to promote powerful economical engines so why don't they modify the engine settings on cars sold in this country at the pre-delivery check through the OBD port. The chip boxes basically intercept the cars ecu signal to the injectors and fool the engine, one way is by telling the engine the air temp is lower than it is so as to inject more diesels and thereforeget more power. So you can get more power but there are no free meals, additional power and torque has to be handled and that erodes clutch, engine and gearbox life, if you accept that, you have a more powerful car. Regarding improving mpg the sellers of these boxes just want one thing and that is you're money, if by telling you the mpg is improved as well as power it has to be taken with a pinch of salt. Were the boxes are fitted physicallycan only be fooling the injectors so regarding getting into the higher gears at lower revs is only possible on manual gearboxes the autos will stay unchanged. On the manual boxes you can go into the higher gears sooner because you have more torque, but the only reason you have more torque is that you are burning more fuel, so that balances out. Also if you drive steady to up you're economy you are not putting in as much diesel in so why bother with the box, if you use the box for the power you are using more fuel so down goes the MPG. If you are still blinded by the sales talk send them you're money, But also send me £5.00 I can make you live for ever, HONEST