Computer problem
2000 Dodge Intrepid 6 cyl Front Wheel Drive Automatic 94000 miles
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My check engine light has been coming on and off for a few months. It will stay on for several weeks, occasionally flashing (I assume that this happens each time the trouble occurs), but it will also occasionally go off for a week or so.

It is a 2000 dodge intrepid 2.7L that had OBD II misfire codes:
P0300, P0301pd, P0302pd, P0304pd.
I cleared the codes and drove again, and after the check engine light came on again, I had P0301pd, P0302pd, and P0303pd. The check engine light only flashed once, so I am pretty sure that all codes were set at the same time.
I accidentally erased the codes one other time several months ago when I was trying out the OBD scanner, and I don't remember which cylinders were listed then.

When it happens, I do not feel any stumbling or hesitating in the engine.
I have only noticed it happen when I am on the freeway and have been driving for at least 15-30 minutes.
I have noticed it happen at both high and low RPMs, but I think I've only seen it happen when I was going at least 50MPH

Some history:
The engine was rebuilt about 6000 miles ago (I fell into the infamous dodge 2.7 sludge problem). At this time the spark plugs, spark plug wires, rotor, distributor cap, and other stuff were replaced.
I replaced both the camshaft position sensor and the crankshaft position sensor (because the car would die on me at random times).

I've seen forum posts that blame this problem in this particular car on both the camshaft and the crankshaft position sensors. It would not surprise me if this is the problem (I just got the cheapest of each that Checker Auto had). I am not positive, but I don't think that the check engine light came on before I replaced those sensors.

summary:
- I'm getting several misfire codes.
- I think they only happen when the car is warm from freeway driving
- more than one cylinders get the code at the same time
- other than the check engine light, I don't see/hear/feel any symptoms of the problem

What should I do to isolate the problem?

Thanks,
L.T. Smash