Tach won't go past 3K

[92lxaz]

From time to time no matter how hard I get on it my tack won't go past 3K. It is fairly sporadic, for instance right now it is fine, and will be for a few days, then it will go back to not functioning properly again for a little bit, day or two. I already replaced the ignition switch as I was reading that might affect it. What can I check on the coil side? Any insight on this? Anyone else have this problem, how was it resolved? Thanks.