Pushrod damage or more...? 289 mild

[Three Peaks]

Sounds like most of the usual culprits were already mentioned above. So, a couple rare issues that may come up and things to check-
What type of rocker arm mounts do you have? Pedestal or stud? If you are running aluminum heads, it is possible that the studs are pulling out of the head slowly. Not a common issue, but I've heard it happens.

Check your rocker tips for wear. I have the Comp Pro magnums on my 393 mainly because I had heard instances like yours of the tips on some of the Mag tips having issues on a couple car forums. No way to tell how accurate these reports are, but your wear pattern on the rod end is suspect at the least.

Overly heavy springs for the purpose could also cause some of the rod problems you are having. Did you check if your springs are suitable for the purpose? Proper seat pressure, no spring bind when loaded, installed properly?

Last thing for now- as mentioned above it sounds vaguely like a cam losing lobes. Take a micrometer and set it up on your head on each valve rocker to read at the rod lobe and run the engine through a rotation. Record this for each lobe (16). Hopefully, you know what the lift is supposed to be so you can check your results against the Cam card. If not, at the least comparing each measurement to the others, a few will pop out as being out of a reasonable amount of variance.

That should keep you busy for a while. Once you've checked out all the ideas above and this one, at the very least you should have an idea where this is headed.

Bob