It most certainly sounds like an Opti issue. Way back when, when I started my Heads & Cam project, I replaced my 110k mile Opti with a Summit unit, the car wouldn't run over 3k RPM's and had the same exact symptoms as your car. I eventually took the Summit Opti off, to replace the cap & rotor with an MSD I had laying around for years. When I cracked it open it had all sorts of corrosion and junk on the points. I called up Summit that day, and they backed their warranty on the faulty part and had a new one at my door within a day.
I assume it was from moisture or something that caused the unit to fail.
I put the new Summit Opti-Base on with a MSD Cap & Rotor, with AC Delco spark plugs & wires and the car ran to the moon until I spun another bearing and FUBARED the motor