yes a truck serial number would be helpful

but off the top of my head a couple of things come to mind here...

as edward said, insure the crank sensor is adjusted properly and the harness connecting it is not damaged in any way

also have you done a compression check on the cylinders? see if there is any difference across the board paying close attention to the no. 2 and no. 3 cylinders. its a long shot but a partially blown head-gasket may cause this symptom too.

just a couple of thoughts to ponder while scratching your head :o)