GT3Fed

Seeking some assistance.

I've imported a 1990 Sierra RS 4x4 which spent much of its life in Sweden. This low mileage car has had head work including port and polishing, new pistons (spec not clear from service records), a -31 actuator, Big Greens, large diameter exhaust, K&N filter and the aforementioned MSD L8 chip. I've driven the car ~900 miles, all on US 91 octane premium fuel and have noted the following.
1. With the installed boost gauge with 50% throttle the boost will max out at ~1.8 bar.
2. With WOT throttle it is impossible to get beyond ~1.0 bar as the engine abruptly cuts off fueling and staggers to get back on but repeatedly cuts off.
3. On start-up the A/F starts at rich, progresses for a short time to stoichiometric and then runs leans after engine fully warm.

California gasoline (better brands known as 'Top Gas') has maximum octane of 91 R+M/2 which I believe has similar properties to RON Octane 95. My questions follow:
1. Is there a MSD L8 specification sheet for the RS 4x4 that can be shared?
2. Is it likely that my California 91 Octane is too low with the current configuration?
3. Are there diagnostics that can reveal map of the L8 in my car that may inform my throttle behavior.

Many thanks,