Here is how the 395 cam idles at 600 rpm with ~16° timing advance more timing made it idle even rougher. At 750 rpm it likes 22° of timing and pulls down to about 40 kpa.
...

Were you running the Black Box PCM or 0411 Silver PCM?

Reason I ask is I ran a Comp cam

258/264 @ .006,
203/210 @ .050,
.458/.458
(.489/.489 w/ 1.6s),
110* LSA, 106* ICL

I have a 395' cam with 1.6:1 rockers in a Vortec 350 powered Express van. I only have 3.73s and run a 4L80E so the gearing is pretty tall. Pulls my 6,000 lbs travel trailer nicely. Mine idled well...