Neon_rt has a good point about the head gasket! These are notorious for going bad on Neons. I had to replace mine on my 98--well on the first engine
Did you or have you seen any leaking oil in or near the spark plugs/ tubes. This was one of the first things that happened when my head gasket blew. I'm crossing my fingers that this isn't the case for you.....it probably feels like you've replaced everything else at this point.