Filling up gas tank problems

I am having a problem filling my Workhorse chassis gas tank. Let me start off saying it always was a little slow to fill, had to find the happy point of correct angle and correct flow speed. This last attempt took me a half hour to put in 15 gallons, kept shutting off every time I pulled the trigger and did back splash twice on me. It was a level location at Sam's Club and never had this happpen this bad. I had a mobile mechanic come to my home and pull the entire gas fill tube, 9 feet, and vent tube off, ran air and a rubber hose through the lines and was determined there was no obstruction. He also visually checked inside the tank and saw nothing that would cause the back up. He did feel that there was possibly not enough of an angle to allow the gas to flow freely into the tank, which I agree that the angle is slight. He took the last portion of the fill assembly( 1 foot piece where nozzle is inserted) and is going to try to find one with a shorter angle that would provide more of a down hill slope. It seems to make sense but just curious if anyone else has or had this problem and have you found a solution. I might add that I first suspected a faulty nozzle on the pump but I returned with my truck and used it and it worked fine. I know one way would help and that would be to raise back end with my jacks but that wold be a last resort. Any comments or suggestions would be appreciated. I have owned this MH for about 8 years and this has just developed. I might add that the tank is not full, should have been able to add a total of about 50 gallons. Thank you, Don.