Well, it's my turn to ask for suggestions..

moper asked if it has valve rotators on the exhaust springs. There was no answer. You want help, you need to provide answers. Valve rotators on ANY type of performance cam will result in poor performance, as those springs designed for rotators are weak as light beer.

Also, you said you've had a max of 16* initial timing so far. Still WAY low for the engine you have which is guaranteed to be less than 9:1. Probably somewhere real close to or maybe even "under" 8.

With that kind of compression, or the lack thereof, a high initial timing setting is the way to go. .........regardless of cylinder pressure.......which seems to be pretty dang good.

It's all in the timing. Whether it's not enough initial, whether you're reading it wrong (happens to the best of us) or whether something's amiss with the camshaft timing.

Probably do you well to get the degree wheel out if more initial timing does not help.