My right side turn signal is not as bright as the left side.

When the headlights are on it flashes slower than the left side.

Is this likely a ground issue, or could something else be the culprit?

Yes, most likely a grounding or clean connection issue. Follow the wires to the turnsignals and make sure that the connections are clean and secure. Headlights have no operational connection to the turnsignals. Make sure the bulb base and fixture sockets are clean.

^ this is probably the issue.

I experienced the same thing with mine. I ended up swapping buckets and that corrected the issue. Too much corrosion that I couldn't seem to clean to get a good connection.

Thanks

I suspect it may be in the bucket as had resoldiered a terminal that broke off and it was kind of iffy.