Pilot/Flying J generally has much higher prices than regular gas stations. However, there is a Good Sam charge card that gets a nice discount that actually makes it cheaper. The problem is that both times I attempted to use it, I wasn't given the discount. Someone from Flying J /Pilot contacted me after I posted here and I got the discount on my account.
IF you can get the discount to work, it's not a bad deal at all. We have also found some independent truck stops that are at least 20 cents a gallon less than regular gas stations.
We generally use the truck lanes. There is no confusion there about fuel type. They are all diesel. There was one thing that initially puzzled us: we were asked if the fuel was refer or tractor. Always answer "tractor" or what choice is not "refer". The refer fuel is the same diesel but untaxed and is generally dyed pink. You can get a big fine if you are pulled over and a trooper checks.