I had that problem on my old Roadster ( 2005 ). I had to replace the filler hose. It had a smaller vent pipe tee'd off, going to the vent connection. The original hose had the smaller pipe left full length, resulting in a loop which formed an air lock. I cut the new one down so that there was a fall all the way to the tank & from that day on, it filled at full pump speed
I don't have any problems with the 3.7 Roadster. I notice that the vent pipe now comes from a connection on the filler cap assembly. I'd check that the vent pipe does go down hill all the way to the tank ( & also that it hasn't kinked)
Ian
