Hello and welcome to JustAnswer!
The Eco light comes on when fuel economy is highest. At lower RPM's, when the torque converter is locked up, low throttle situations will all turn this light on. This isn't any sort of added system, the light is just turned on when the van is in the correct conditions for better fuel economy. Altering your driving style so this light stays on will give you better mileage.
If you had a 3.3 or 3.8 in your last van you've got the same engine again. There were a few external changes to fit the new minivan's engine compartment requirements, other than that it's the same. The engine may seem louder than what you are used to because of the new 6 speed transmission with the RPMs higher under acceleration and more shifting going on.
As far as mileage you'll want to give it time to break in. Fuel mileage complaints normally aren't considered until the vehicle has past it's 12,000 mile break in period. Other things that affect mileage are the cold weather, ethanol blended fuel, warming the engine before driving the van in the cold weather.
Thank you for a quick answer. My engine has only four speed transmission as the old one. I think six speed is only for the 4.0 L engine, but your answer satisfies my request.
I also find that the headlights are not bright enough, especially when you drive on highway, without enough streetlight. Do you think that I can change for a better bulb,aftermarket bulb. IF YES, WHICH ONE SHOULD i CHOOSE. Please help me also on this matter.
Thank you very much.
Make sure the headlamps seem to be properly aimed. If they are too low or high they may appear to be dim. You should be able to find some brighter bulbs for your van without much trouble. I haven't personally installed any aftermarket bulbs in any of these new body style minivans yet, so I wouldn't be able to give you an honest recommendation on a specific one to buy. If you have a large parts store nearby like an Autozone, Pep Boys, Advance, something like that, they will have a large selection of bulbs that will be brighter.