Ignition control module. It's getting heat soaked.
The Opti would show up more around high-RPM misses at first 90% of the time and work it's way down to the lower RPMs, but usually doesn't cause a no-start condition.
Remove the coil bracket bolted to the block behind the intake ducting in front of the driver's side head and remove the control module, which the black rectangular thing. Clean the mounting points thoroughly, reapply a small film of dielectric grease, an see if that fixes it. MAKE SURE you have all of your grounding points down tight on the bracket as well and to the block. If this doesn't work, drop the $30 on a new module.
Step two (if the module doesn't do it): Replace the coil itself. Same bracket, similar procedure. $35 for an aftermarket unit from Jegs (LT1s like Accel or Mallory). Don't use MSD. You've been warned.