340 Engine Shake

Phreakish said

In the fitech dashboard, do you see anything change when the shake happens?
Does afr suddenly drop, or rise? What about map?

What about exhaust LEAKS? I was convinced I had none, but I did and the symptoms were similar to this. Of course any issue with the fitech and the idle would do something similar..
Do you have a vacuum line hooked to your fuel pressure regulator?

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That's the thing, there are no visible signs. I did a data log and nothing changes. No dips in vacuum, AFR, rpm, nothing. I also used the large Guages feature to monitor that while it happens and no changes. I don't think I have any exhaust leaks. I used remflex gaskets on headers and collectors, everything else is welded. What is a way to check check for exhaust leaks?