gettin bad mileage .. replaced o2 sensor and cadalitic converter cause it was blocked up ... it got excellent mileage 1 year ago.. is it time to replace the EGR? it has 155K miles on it ..runs like a champ but sometimes uses oil like half a quart all at once then dosent use any for weeks what is wrong with it.. should i put it on a lift and drive a new one under it ?