1996 Dodge Intrepid 3.5L problems galore

Please help.

I drive a 96 intrepid with approximately 100k miles. For about a year, it's had problems galore, but always ran. My check engine light is constantly on, and reports misfires. I have replaced the o2 sensor, and another sensor I can't recall the name of right now, the engine computer, the injectors, spark plugs, spark plug wires. Most recently I replaced the injectors, the car runs. At low RPM, and speeds around 45 mph, it rumbles and shakes real bad. Today, on my drive to work (approximately 60 miles) the check engine light flashed the whole trip. What else should I try?

edited to add: I believe it was the cam and crank shaft sensor I replaced. Also, I've been told not to drive it if that light is flashing. I've also replaced the timing belt recently. Any other tips?

edited again to add: I just took it to auto zone to get the error code readouts. They are p0300 p0304 and p0171.