I'm trying to understand just how screwed I am. Took my '03 Civic EX to get codes read at Sears, came up with P0340, P0341, and P0420.

I've driven long distance twice this week (150 miles round trip). On my way home today, the CEL came on. I had a bit of rattling, and I stalled once at an intersection. I was about 60 miles from home and the car would shake as if it were going to stall at around 70 MPH. It did fine driving at 60.

Then it started having problems in lower gears (stick shift) from a cold start. Lots of jerking and rattling if I hit 3000 RPM. The weird thing was that after 10 minutes or so, the car drove fine. No rattling, no stalling, nothing.

From what I've been finding online, I'm looking at either bad sensors (hopefully) or needing a new timing chain. I'm looking for advice on what the problem sounds more likely to be and what kind of costs I'm likely looking at. Also, would I be ok driving to my mechanic or do I need to get a tow?

Thanks in advance for helping out my mind at ease.