2001 Mitsubishi Eclipse 2 YEARS LATER FIRESTONE STILL CAN'T

I have a 2001 eclipse. I've had it for 2 years now. I have kept up on all maintenance requirements, and have had various diagnostics done since I have owned the car. When I am at a light, or I am at a stand still, my car juts forward and shakes, almost like it is going to shutdown right there. I have had a diagnostic done everytime I go to Firestone for preventive maintenance, and they still cannot tell me anything new. I believe it is the oxygen sensor, eing that it is after 60,000 miles, and I stongly doubt the owner got these thing changed out. When I bought the vehicle it had 64,000 miles on it. Any suggestions before I buy a new oxygen sensor?