F-Jape

Okhay, so I'm running out of ideas what's the problem. I'm new to these MSD boxes.

I bought new 6BTM Ignition box in last March and can't get it working properly. Here is link to vid showing the issue: It won't stay idle under load and sometimes even neutral. It has given two times code 42, refers to EST circuit? I have tried with the EST wire disconnected and runs well w/o problems. (Of course haven't driven while EST is disconnected)
Box's power input wiring are connected straight to battery and coil end with MSD #8876 wiring harness and connected like the instructions shows also I soldered connections. Tried already to run the wires separately from coil to box.

Car is running fine w/o the box

After the vid I thought that it could be low voltage under load. So I replaced new alternator, made new battery wiring connections and good ground also run another thick wire from alternator to battery, with no luck. Battery is one month old 74 aH Bosch.
Voltmeter shows w/o the box connected steady 14,4 Volts at idle and under load. With the box connected it shows steady 14,4V at idle (when it's steady idle) and jumping between 13-14,4V under load (when it starts to hesitate), never went under 13V. Measured from battery.

Already asked from Finnish F-Body Forums and search topics in here, no one seems to have same kind of problem.
Any ideas here?

And the car's background info (will list only which refer to ignition system):
Well maintained and in good condition, summer driven. (Hobby car)
1989 Camaro 305 TPI Prochargered
MSD 8366 Distributor (New) and I have replaced ignition module.
8,5mm Moroso wires
Hypertech coil
Delco R43TS plugs .035 gap
6* BTDC
Burnign own PROMs, haven't done anything spark modifications except disabled Highway spark. (Already tried older prom where they are enabled)

F-Jape

Problem solved, coil was done