Thanks for all the replies.  Generally you comments make me feel better about my current mileage results.  At least gas is cheaper this year compared to the 3,600 mile trip we made to Georgia last year when gas prices were (more or less) double what they are now.  There are afew things here that I'll look into further.  I'll even try keeping speed down, although I'm not a heavy-footed driver.  As someone said, I'm not interested in spending a lot of cash to save a few bucks in gas costs or trading for another truck when my 11 year old, low mileage, paid-for truck is fine in all other ways.