Thanks to all for ideas and comments. The HEI was installed before the tach was installed and the dealer said the tach would work with HEI distributors and it did until last week. I drove the car this morning and I don't have the erratic movements, but the needle doesn't move until it should be showing about 2500 RPM. Proportionate response seems to be occurring after that. I contacted The Parts Place this morning but haven't heard anything back as yet.