I have a 3.8l from a 1975 Skyhawk that doesn't seem to be running right. There is a vibration that is noticable from the interior that varies directly with engine speed, whether the car is moving or not. It almost seems like there is something out of balance with the engine. This is the first time that I have ever driven a car with this engine, and I know that they may tend to shake, which is why Buick switched to the even fire design. While I know that there are a lot of variables involved (i.e. motor mounts, flywheel, clutch, etc.), I was hoping to hear some feedback from anybody who is familiar with the running characteristics of these engines. Any feedback would be greatly appreciated. Thanks, Dan