Bone-stock 1978 SBC 350 with about 75,000 miles on it. When I dropped it into my '53 Chevy 12 or so years ago I put an Edelbrock Performer manifold and 600cfm carb on it. Otherwise it's totally original. It's no powerhouse, but it has always run smooth and quiet. In early November I filled up with 91-octane gas from a place that claimed their super unleaded had no alcohol, and at that time I added Stabil as well. Since then I've driven the car to work once every few weeks. Always starts right up, always runs great. This morning when I fired it up (and it fired right up immediately), it was idling a little rough. By the time I got the main road a mile from my house it was barely running. The whole rest of the way to my son's daycare (a couple miles) and then the rest of the way to work (another 10-15 miles or so) it was running lousy: Shaking and bucking. It was so bad at idle I had to put it in neutral at red lights so it wouldn't shake the whole car and so I could give it a little gas to keep it running. Going down the road I could feel it surging and bucking, which it has NEVER done in 12 years and around 20,000 miles. Any idea what is going on? I was hoping my choke had stuck closed but I pulled the air cleaner and it is wide open as it should be by the time the car is warmed up. I did stop and add 8 gallons of gas from a Sunoco station, hoping the off-brand gas I put in my car? It seemed to smooth out a bit just as I got to work but I didn't have time to drive around to really see what was going on. So I'm at work now with no time until the end of the day when I have to pick up both my young kids and take them home and for the first time in years I'm worried that the car will die on me. HELP!