I don't have a turbo, but the 4wd hurts mpg a lot, and your truck is about 1k#s heavier than mine. You also have an automatic.
Before I started modding and hypermileing I was getting about 15-17mpg too (assuming odo is accurate) - in fact I never got as high as 19.
I have also found that towing hurts mpg much more than having a load in the bed.
Have you checked the link to my instructable or my post here that details what I've changed? I've removed all belt driven accessories (including alternator), installed coroplast underbelly tray/grill block/wheel well covers, among other things, and I EOC at
every possible opportunity (which I assume, having an automatic, you never do)
With each change I saw a slight improvement and gradually gained about 10mpg. If the odo is inaccurate and I was getting only, say, 12-15 that would still put me around 22+ now.
Today I'll check the odo vs. g-maps. I just ordered a GPS last night too, (which even keeps track of mpg if you tell it gallons of fuel at each fill) so we'll have a more accurate calculation (to not believe
)