I did get gas at a different place this past time(Shell) and I am overdue an oil change and plugs. And come to think of it I did go into a store and left the wife and kids in the truck the other day with the truck running and A/C going for about 20 minutes, so that doesnt help either I'm sure.

Yeppir, 20 minutes of 0 mpg will certainly pull down the mileage, much like warming up in the winter.

Sounds like you are on to something.