Its not that bad... well, taking it in all at once is!
Let's start looking at what is wrong by moving system by system.
First, have you replaced the thermostat ever? If so, you could have had coolant leak over the Opti-spark and that could create a moisture problem in the Opti-spark.
Next let's look at fuel pressure. Do you have a gauge? Do you have a shop manual for your car? Check your fuel pressure on the fuel line. Make sure it is creating enough pressure and not bleeding off to quickly after power is shut off either. Check your pressure on the rail. Ensure the vacuum line is connected to the pressure regulator and the intake. Leaky injectors will show up with tell tale signs on your plugs.
FYI- even a bad fuel pump can sound like it is working. When you rotate the key forward, you should hear the pump engage. It should sound like a monotonous buzz for about 3-5 seconds. If it doesn't sound like an even buzz, the you might have a problem.
Check your plugs. Make sure your plugs have an even amount of wear. If one is suspect, check your wires and replace the plug (and perhaps a wire). If a new plug and wires don't fix it and its not the opti or the fuel pump... then it could be the opti.
If the fuel pressure, spark plugs, and a compression test indicate everything is okay... very well might be the Opti-spark. You'll need to connect a scan tool and watch the 02 sensor reading from bank to bank. When the 02 sensors fluctuate wildly, the ECM will try to compensate by adjusting the advance etc. However, all of the ECMs actions won't be enough when moisture scatters the light beam in the Opti-spark. It won't trip the check egine light either. You may see a noticeable drop in the current on the car as it essentially crossfires. It will be also be intermittent and seem to strike when least expected.
Although I don't have an LT1, I did have a 94 Firebird Formula with the LT1 and the same problem. I replaced a fuel pump and wasted all kinds of time trying to figure that one out myself.
The Optispark is easy to replace. You'll have to drain the coolant, remove the accessory drive belt, intake ducting, and numerous small parts- but I'd rather do that than replace a fuel pump.
If it is the Opt-spark, Jeg's carries a couple of kits to replace the OEM parts. MSD makes a replacement unit as well. They aren't too costly either.