Yep, me too. I was skeptical at first and actually called the dealer to see if I had to do acalibration on the overheaddisplay. I drove this one-ton back and forth 5-6 days a week from my house into the bay area (about 146-148 miles one way) and it was usually at 4:30 am so traffic wasn't too bad. I did this for 5 months straight and got usually 655-680 miles to a fill up. I read in the book it has a 35 gal tank. I never ran it out completely but I have ran it down to where the overhead said I had less than 10 miles to go till MT. I figured it'd take about 34 gals or so to fil but never got more than 30-32 in it, takin my time as you stated and those are the honest to God numbers. Now if I let me wife drive it to Sacramento, (also flat ground, lead foot, window open, hair in the breeze style she's usually drivin in, well those numbers are in the crapper. She's lucky to get 18 on the fwy!
I'm not a "hot Rod" kinda driver but on occassion have been known to put a Mustang 5.0 in the weeds! LoL.