Need recommendation for a Carb for better MPG!

I Live in Lincoln Nebraska. I wish I had one of you guys close enough to hire to spend a couple hours with me and my Demon to see what might be going on because there are other symptoms that might make a diagnosis easier.
I sure appreciate all the replies! THANK YOU!!
If you will follow instructions, we can help you from here. But understand, there may not be much room for improvement if your tuneup is right.