how come large car company`s cannot get better than 20MPG from full size vehicles?

they probably could if they wanted too,but it seems like their working with the oil company's sometimes,because every time the government says they need to get better mileage it seems like it gets worse,you can fine tune any vehicle made and improve the mileage on it,so it does make you wonder about this,it almost seems like their not trying to help with mileage,good luck on it.

Well first of all you have a cummins diesel and the diesels get better gas mileage. Secondly, my neighbor has a Lincoln towncar and he says that he gets 29-32 mpg on the highway and about 25 around town. The buick park avenue and lesabre also get 29-30 mpg highway.

That's a diesel. Massive torque helps it move heavy weight more efficiently, and diesel fuel contains ~10 percent more energy by volume than gasoline. If you're comparing to gasoline engines, you're doing it wrong.

And they CAN get better than 20mpg...in fact they mostly DO in cars. Just not better than 25 mpg for the big ones.

This is because people just HAVE to have more power. Buyers of new large, $30,000+ cars are going to be more put off by a car they perceive as "underpowered" than they will be by poor fuel economy. So you sacrifice economy for more power.

If you're just talking about trucks, it also has to do with the fact that they have barn-door aerodynamics, and the fuel efficiency difference between gasoline and diesel engines gets bigger as the engines get bigger.

Its not that large car makers cant get build better mileage vehicles, it all comes down to money. They've made cars that can get over 50 miles a gallon since the 70s but theres huge money in Oil and that will get hurt if cars were more efficient. They will slowly release higher mileage over time to maximize their profits.

because you sacrafice stuff for your mpg. im not sure what your "tuning" but it would help if i knew that. Are you talking about physicaly tuning under the hood or taking a programer and screwing with it that way. Do you really think that car companyies such as ford and chevy would WANT to loose sales due to how good of gasmileage it gets? American car companies are loosing major profits because of this, trust me they would fix it if they were trying to make a profit thru oil companies.

They could if they wanted to but then the oil companies would get mad because demand for their product would drop. Oil companies and car manufacturers have each others backs, to our detriment as consumers.