Bucking and stalling in a 95 Lumina

I had my car serviced a month ago because it would start bucking and eventually stall. At first it wouldnt do this for the mechanic and nothing was showing on the computer. After the mechanic had it a few days it started to do it all the time. Many things were checked and changed. The mechanics narrowed it down to rebooting my computer and also replacing ignition control modules among a few other smaller things. It ran great for a month but now my car is doing the exact same thing. It bucks so bad that my friend who was behind me thought she was in a rap video. When it starts to buck it feels like the gas isnt catching and the car looses power and stalls. Now I'm being told its the EGR valve. I dont understand how I can have the same problem but now I'm being told the cause is from something else. The symptoms my car is disaplaying seem to be pretty drastic compared to what I've read on this sight about EGR valve symptoms. My symptoms sound more like a plugged exhaust system but my exhaust system was checked. Any one have any input?