Paco,
I use the "Bully Dog" system. It plugs into the diagnostic port under the dash...you follow a step by step install program much like any other computer program. It also reads defect codes, calibrates the vehicle computer for changes in tire size and the like. It also allows you to change selections for various things like auto lock, auto shut off of lights....torque curve...fog lights on with Hi-Beams...all sort of things.
Cost is about $550 and works on Ford, Chevy, and Dodge diesel engines.
It is continually updated without charge by going to their web site and logging in.
It is impressive to say the least. The test to confirm the mod is installed properly is to test drive the vehicle by accelerating to third gear...push the go pedal to the floor and see if the rear tires break traction on dry pavement.
It also does it in four wheel drive....must be horrible for the drive train!
I went from 17.8 mpg to 22.9 mpg as measured on consecutive tanks of fuel.