Toyota Repair: 2002 Sienna fuel tank wont fill, flapper valve, vent tube

Question
2002 Sienna Symphony w/71000 miles. A few tankfuls ago the gas cap was not tightened correctly and made the engine cut off while driving. It would not restart until I figured out the problem. I had no problems for the next 2 fillups. On the 3rd fillup, the gas could not be pumped at the normal rate of speed. The fill tube would fill up with fuel faster than it could drain into the tank. I don't know if one thing has anything to do with the other. I was told that it could be a kinked vent tube but I traced it back to the tank and it seems fine. I noticed that there is no little trap door in the grate at the top of the fuel fill tube but I don't know if there was one there originally. Ques1 Was there a trap door there originally? Ques2 Would this be covered under warranty? Ques3 What difficulties could I expect with disconnecting the fill tube at the fuel tank and checking for blockages?

Answer
No there was no trap door originally.
The veh is out of the comprehensive warranty(3yr/36,000)
You can remove the fill tube just make sure that the fuel level is at 1/4 or lower, inside the pipe on the tank may be a one way flapper valve, there is a possibility that it is stuck or that there is a foreign object in the filler tube or the pipe on the tank, it could also be a vent tube restriction so check the vent tube attached to the filler tube.