problems with fuel pump?

Had fuel pump replaced 3 months ago, been running fine till this week.
Had trouble starting engine early one damp morning started after cloud of white smoke, ran very erratically as if fuel not getting through properly!
Later that day engine cut out completely, would start then just stop. Had diagnostic check and came up with crankshaft sensor, replaced that, ran ok for 2 miles then started missing again, diagnostic check showed nothing, freelander runs ok on motor way if thrashed but normal road speeds it still misses! any ideas because fuel pump only had 3 month warranty we think so need help!!!!

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