360 stalls on deceleration from throttle blip

Ok so I bumped it up to 15 still doing it. Should I try higher? I don’t know anything about the rebuilt motor as far as cams. I suppose I should check compression, I did notice some aftermarket rockers when I pulled the valve cover to get TDC when I went to install new distributor so work was done to it. I know the previous owner ported and polished the heads. I don’t have a tac installed I just know the rpm from timing gun at idle but it seems to drop quite a bit in drive and also that seems to be what is happening after I blip the throttle and let off the gas fast the rpm drops way low though I don’t know how low without a tac.

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