The fuel efficiency of International's Navistar truck line depends upon how you set the electronics and how the driver operates it. The most efficient ones are the Paystar line, which are also the smallest. International makes a full range of over the road trucks.
Www.utoGuide.com has a list of the top ten most fuel efficient pickup trucks for 2013. Www.shopautoweek.com also has a list of its top four most fuel efficient pickup trucks.
A very straightforward guide to the best fuel efficient trucks can be located at http://www.autoguide.com/auto-news/2012/02/top-10-most-fuel-efficient-pickup-trucks.html. It gives details on the best MPG trucks of 2013.
There hasn't really been a brand of semi trucks recognized as the most fuel efficient. Since they run on diesel a more efficient fuel, semi trucks already are more fuel efficient than cars in terms of size and power.
Hybrid trucks are definitely more fuel efficient than conventional gasoline powered trucks. Hybrid model trucks generally have up to 25% better fuel economy than their gasoline alternatives.
There are a number of different trucks that are safe as well as efficient. For a woman with children I would recommend a Ford or Toyota truck for her to purchase.
US News has the ranking for the best efficient cars. You can read them at http://usnews.rankingsandreviews.com/cars-trucks/rankings/Affordable-Small-Cars/
ford has sold most pickups
The superlative of efficient is "most efficient."
Aside from the Dodge Ram series and now discontinued Sterling Bullet, it's available in a wide range of medium and heavy duty trucks by most manufacturers - Freightliner, International, Ford, etc.
Spur Gear is the most efficient
The most fuel efficient GMC Truck you can get it the GMC Banarge, it can come with a small 1.8ltr Diesel Engine offering upto 25Mpg, tho this truck is rather slow it can be great for starter businesses to save on fuel costs
Cars have a smaller engine than most trucks. Because of this fact, cars require less gasoline to power itself than a truck does. A truck, on the other hand, requires more fuel to power a larger vehicle.