Ford Aerostar Oxygen Sensor Replace/Remove

Hi The Problem Started A Week Ago, The Van Was Running Fine, Then All Of A Sudden It Started To Idle Rough, When In Gear It Is Much Worse...

Cargo Van, 3.0l. Complete Ford Long Block Installed 70000 Mi. Ago. Rebuilt (completely)a4ld Trans. Recently. Runs Good, Major Tune Up 25000...