I assume you have a GT cause that is where you posted it. And for the record, quite a few have hit over 300k miles. So you should be able to.

But first thing I notice is the flashing SES light. This means that you have multiple misfires. So my guess there would be spark plugs and wires. Sounds like you changed the spark plugs. How did the ones that came out look? And did you change wires as well?