Shift light comes on at 5600 and the gauge says 6100. Which one is right and has anyone else ran into this?

I would trust the tach i think my shift light is a little off also

Tachs can be laggy, especially in lower gears. Found that out in the Honda; the tach was reading below red-line in 1st when the rev limiter cut in.

--DD

Any chance you are using a MSD with a tach-adapt?

I do and my tach bounces now and seems to lag a little

Trust the one that you tested to work correctly.

Not running a MSD right now. I did switch the pills and received about the same data. Off by 500 RPMs.
One of the mechanics at my parents shop has a digital test light and I think it shows the rpm range on it. Maybe that will answer my question.

Shift by ear.

Rev it until the engine blows, then back it off just a hair.

--DD