340 Engine Shake

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?

With the car cold, and you key on the system. What does afr read? Don't start it, just key on.
Should start at 14.7 then climb to 20.1 and stay there..
A bad sensor will just stay at 14.7

I'd do as inertia suggested to check for leaks.