I have a 2005 2500hd d/a with a high bed cap and all I can say is WOW. The power combined with the fuel ecomony makes this an awesome truck. I asked my buddy how the truck pulled my 26 ft enclosed trailer with the car and he replied "what trailer". Man he was not exagerating. Tons of power. I found at 60 mph on a level grade my truck dic says 23 mpg.It droppes to about 19 at 75. These trucks have alot smaller power band that a gas vehicle so fuel economy will suffer the faster you go. If you want the best fuel economy you need to keep the rpms at peak torque with I believe is 1800 rpms. The engine is most efficent there, that is why it has the most torque there.