Over the past week or so I've redone the front end on my 06 4.6 and changed the plugs(not too horrible but off enough on the gap). No leaks that I could see but was a little under a quart low after 5k. The truck has been a reliable daily for 7 years now yet I feel like the next big issue may be just around the corner. What should I start checking more proactively to keep her going?