Dealer replaced 7 fuel pumps in 7 years,they say intermittent problem unfound,

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Bought car at 40,000 miles,at 60,000 miles fuel pump replaced.there are 6 more replacements after that.Around 20,000 miles it cut off.They say the problem is intermittent and can't find it.So just replace pump and send me on my way.Only to come back with the same problem.I'm on highways alot and without no warning car cuts off just like that,leaving me stuff in the middle of traffic.This is a safety hazard.What is the problem before it's too late to fix.