Average cylinder pressure of 152.5, which you call; "so the compression doesn't look all that bad", by itself is barely Ok for whatever is in it now. The only thing that is saving your combo is the 3.91s, and possibly the TC as we don't yet know the stall.
So whatever cam you chose it is gonna have to be custom, and you are gonna have to figure out first, one of the following;
1) your exact compression ratio, or
2) the exact ICA of the current cam,
3) both would would be ideal.
From those numbers you can build a cam.
Without those numbers anything you put in there is a gamble, and is likely to turn your bottom end to slush, mandating a new TC. And then your fuel economy will take a dump as well.
Unless your low cylinder pressure is already the result of a big cam.
So I highly recommend a LeakDown test to prove the numbers are NOT due to leakage.
Without some kind of idea as to what's in there .... IMO, you could be setting yourself up for an expensive disappointment.
From what I'm seeing, that engine is already a candidate for being a soft combo.
Those early 340s in stock-tubbed As,with street tires,are tire fryers all the way thru first and a good ways thru second to something like 60 mph,often even higher. How does yours compare?
