I am so confused. Please help.

[dwaite72lnghrn]

First verify the rear end. I thought most 3/4 tons had a H052 or dana 60 in them. H052 pretty much eliminates a gear change. Dana 60 will give you more options if you are thinking swapping gears. And anytime you go 65mph the truck is a big brick being pushed through the wind so MPG will drop because of the resistance. 14mpg could be a target, I would go with taller tires. This is the cheapest way to drop rpms. Get a vacuum gauge and use it to keep vacuum up just a little pressure change on the gas pedal will give a big change in vacuum (fuel economy) with a little drop in speed. Remember to correct for the tire size with your speed and mpg calculations. I have heard of people making changes to tires or gears and never change the speedo gear and said the MPG was the same, until they added the 15% change in miles driven.