Gas pump clicking full repeatedly. :(

Planetcat

Test Drive
2002 xTerra 6 cyl. Had some water in the gas tank, so I had the tank drained and system flushed, along with new sending unit, fuel pump, and spark plugs. Now, when I go to fill it up, the gas station pump clicks like it's full repeatedly. Took 20 minutes to fill it last night. This is happening at multiple gas stations and never happened before. What do you guys think? Did my mechanic not vent it properly and excessive backpressure is triggering the gas pump to stop? I will bring it back to him, but wondering if anyone has any ideas. Thanks.
 
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