Our rig sometimes does that. It seems to be more likely to do so after being on the road for sometime (6+ hours, summertime). So I always wondered if it was related to the gas in the tank being hot and the vapor pressure being high. The issue usually seems to resolve itself after I can get about 15 gallons or so into the tank, which I figured cooled the fuel down a bit. Seeing as the slow fill issue doesn't happen too often, it makes it a bit more puzzling and difficult to figure out what's going on. (I've EVEN been tempted to blame this dang "ethanol" gas they force us to use as being the culprit, though I doubt that it has anything to do with it. Though....I don't remember ever having this issue back in the early days we had the motorhome, before 10% ethanol was required.)
That said, I HAVE found at times, as others above have pointed out, that rotating the fill handle can often solve the problem and filling resumes as normal. I don't know if this is because it allows better venting out the fill pipe, or if the gas "sloshes" differently down the fill pipe, but it seems to work. I keep telling myself that "one of these days" I'm going to see if I can figure it out. I have looked at the filler area and don't see anything obviously wrong. But....one of these days....LOL
~Rick
2005 Georgie Boy Cruise Master 3625 DS on a Workhorse W-22
Rick, Gail, 1 girl (27-Angel since 2008), 1 girl (22), 2 boys (23 & 20).
2001 Honda Odyssey, Demco Aluminator tow bar & tow plate, SMI Silent Partner brake controller.