Electrical Issues at 2500 RPM

Hi Folks,

Here is my issue - 1984 Duke 4 speed - When first started car runs nice and smooth. About 10 minutes into a drive, around 2500 rpm car begins to buck and the gauges start to be come erratic - speedometer spins completely around, rpms on gauge and volt gauge also erratic and I here a "ding" from under the dash probably because of the gauges. I just installed a new coil as old one was a little out of spec doing an ohms test. Car runs fine, actually very smooth as long as I'm under about 2500 rpm. Doesnt matter what gear and pulls strong in 4th up hills - again, under 2500 rpms. I'm thinking a grounding issue but nothing is visually apparent. Also replaced wire from coil to cap. I'm lost here and value your thoughts and guidance. Thanks!
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