tallsc

I am looking to purchase the 2014 Nissan NV 2500 HD with the standard roof and 6 cylinder engine. I will be carrying 1000 - 1700 pounds of tools, etc. on average while driving mostly highway miles over flat terrain. The weather is generally nearly 100 degrees Fahrenheit in the summer and rarely drops below 30 degrees Fahrenheit in winter. How many miles per gallon can I reasonably expect to get given the parameters above?