Cadillac stops after 20 mins.

I own a 1993 Cadillac Brougham. We had the knock sensor replaced and it started cutting off, after driving it a few minutes. We did not drive it
for a year after, and was told, after some time that it was the Fuel Filter that caused the car to go dead. We replaced the Fuel Filter, but are still having the same problem. Please help! What is your expert advice for this problem.
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