brief sound like going to throw a rod

What is your question?

It first made sound for a couple seconds at about 45k mi at start up, then again about 15k later and then around 75k. Since then, a couple times it has run rough for several miles before clearing up. once since then, it started up like it was running on 5 cylinders. I run Royal Purple 5W30 in it and change every 10k miles, with a new filter at 5k. My mechanic suggests a pre mature lifter failure. any suggestions?