Welcome to the forum Sam.
I don't think that GPS's have that capability yet because there is such a turn over in Fuel stations through out the country now. Truck stops seem to be your best bet if your concerned about length. At 250 miles or so I start looking at bill boards for a Love's, TSA or Pilot station but I'm also looking ahead at stations that I can see from the highway.
California is one of the hardest states to find one because of the road sign restrictions.
I've been from South Florida to California and parts in between and have not had any real problems yet but stick pretty close to the interstates and major highways.
Good Luck and again Welcome.