One of the problems with many RV's is the location of the fuel filler and fuel tank.
The tank is between the rails, About a foot below the filler in many cases.
The filer pipe is quite long.
The result is there is not enough SLOPE to the filler tube to move the fuel into the tank quickly enough.
NOW: if the vent line is not clogged (Which will make a bad situtation much worse) try this.. Drop the pump-side jacks, On my coach it works best if I drop the pump side REAR jack.
It also helps if I scope out the pump islands.. The above is used if the site is level.
IF, however, I find an island where the spot I park to fill slops away from the pump, and even better down (toward the front) and away... I pick that pump.
Since just now I tend to have only a few places I fuel... I have learned the best pumps for a quick fill.
Home is where I park it!