Someone please help. Motor is a 327 SBC and when I cruise around 3200-3800 RPM it runs fine and then it goes duh-duh-duh then runs fine for a little longer and then duh-duh-duh. When it is doing this, if I open it up all the way, it doesn't do it. I've had the distributor curved, and it did it before and after the dist. work was done...
What do you guys think it could be?