I had my 250hpdi in for the new oil pump replacement , and now running @ WOT the motor feels like it is surging, It still comes out of the hole and has good midrange but it now will not turn but 5100 R's it was turning 5850 . I am leaning toward a fouled plug as they have to dump all that extra oil through the system when changing the pump, but wouldn't that hurt the hole shot as well if it were a fouled plug???