If it truly a stock motor thats likely too much initial timing.

Have you tried the max vacuum test to see what the engine requires. (up the advance until max vacuum is established then back it down 1". While doing this you will need to keep adjusting the idle rpm).

Whats the cam duration @50?

If it's truly stock then 10-14 initial would be more appropriate. Depending on which heads but 38 degrees may be too high and depending on which springs are in the distributor your curve may be too aggressive.