I have a 1975 class c and it's very difficult to gas up. At the lowest pump speed, I have to stop every half gallon to allow the gas to go down or it overflows. It gurgles like it's airbound. I can't see any filters on the vent tube at the gas tank, or any kinks in the line, and the access at the filler neck is hard to get to. I can fill it very slowly from a gas can. The filler hose, which is 4-5 feet long runs up and between the frame members and has a factory fitting that may restrict the volume.

Your issue is going to be a low spot or kink, most likely in the vent hose that will trap just enough fuel to for a plug. You must trace the vent line all the way back to the tank and remedy it by rerouting, shortening or straightening. This is more common than you might think.

To confirm this, if you are able to make a 90 degree adapter on an air hose , blow back through the vent in the filler neck until you feel or hear the air back up to filler neck. Without moving the coach try filling it then, if it works you have confirmed the cause.

Good luck
Billy T

Thanks for the info. I did trace it and what I was able to see looks good. Would have to drop the tank to see the rest. It does feel ok. I checked the vent and it's clear. I'll see if it works now. It looks like it could also be the filler hose. It was repaired at one time, and not what I would not call nice. It has a rubber coupling connecting the filler neck to a plastic short pattern 90. It travels a few feet then transitions to a specialized fitting that narrows to go between a frame part? and the floor, then into the gas tank. Is it possible to remove the sharp 90. This would cause a belly in the filler line.