I find different pumps act differently, some I can get a nice slow even fill and some seem to be to sensitive and are either off or filling so fast I get overflow. I don't always get the pump to shut off automaticaly, so I try to listen to the sound of the gas while I'm filling. I can usually tell it's getting near full by the change of the pitch.
Try different pumps, even at the same station, hopefully you'll find on that works for you.
On the road you just have to take your chanses.
Good Luck, T.