Have a vibration...

Since you didn't say i just installed a 360 or i just replaced wires or i changed the trans, you're kinda explaining this as you have been using the car and now today it is having a issue.

So if thats the case and it's not a incorrect firing order i would point you to the flex plate and balancer.
If either of those aren't showing sings of broken, slipped or cracks, then start pulling plug wires till there is a noticeable change.

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