The stock HEI module under the cap is junk, that needs changing one way or the other. You can get a good one for about 40 (accel) or a great one for about 75 (MSD). Go ahead and change that first. Make sure you have a ground from the engine to the firewall and from the engine to the frame. Those missing causes all kinds of crazy problems. The next thing to go to is fuel. Sounds like its leaning out. Check to see that the vacuum actuator diaphram is working and that the butterflies open and no bent linkage. If you have a 3310, order a secondary metering block kit for $30. and a power valve plug for it. Then you can easily change jets. A fuel related miss on the top end is usually a lean condition.