my truck loses oil pressure when warm and the oil light comes on

Suspect sludge build up in oil pan blocking oil pick-up tube//screen after engine gets warm.. Then when engine is turned off..sludge drops away from screen,..upon restart, pressure is ok ..until ..sludge is picked up again, after engine has been running for a while... Sludge will migrate (move around) more aggressively after engine has warmed up... Have oil pressure tested with manual test gauge to confirm...ASAP!!.. This condition is usually attributed to infrequent oil changes//engine service! .. This being the case, only way to repair is oil pan removal to clean out ALL sludge including the pick-up tube.... Good luck.