I think poorva is deliberately delayed in allahabad and kanpur. I observed all trains during that time that includes purushottam sampoorna kranti and vikramshila most of which reaches delhi on time.it is mostly poorva which gets delayed by 1to 3 hours. Also deliberately letting poorva get thrashed in hands of sampoorna kranti. For example yesterday it i saw poorva crossed karchana 1 min early .same train was deyed by 1 hour 30 min just to reach allahabad which was not more than 12 to 15 km away.