I have an 85 Mercedes sedan right now. I like the diesel engine which gets about 27 mpg highway. I am sold on diesel, wouldn't even consider aconventional gas -powered vehicle. I am researching larger family-sized vehicles (used). Is there such a thing as a diesel truck (would have to be extended cab) or a van that gets similar gas mileage, or does having ANY large family vehicle mean poor gas mileage?