Okay I have a 2000 Taurus for last couple years check engine light is on. Autozone tells me code is EGR but...

We replaced the EGR and light went out briefly but came back on later. We were told again it was reading the EGR....so we replaced it again light went out briefly! Light is still on!! Now I am loosing power when driving sometimes and car doesn't shift properly when this is happening and there is also a rattling at same time. I took it to the guy who rebuilt my transmission last year and he thinks it may be the cad. converter. I HATE MY FORD!!! I just don't want to go have this fixed only to have light come on again and it be same thing or something new!!!