...if this turns out to be your OptiSpark, unless you intend to sell the vehicle soon, stay away from nearly every Opti on the market. Summit Racing carries a reman OEM, same unit GM sells with the same warranty *through GM*, for 1/2 the price. I've replaced 7 Opti's in 12 years. 8 If you count one a member here repaired for me.
When my first Opti went out, they were $550 at autozone -vs- well over $1,000 at the dealer. Dealer is still upwards of $1,000 and is not NEW, dealer Opti's *are* reman now. They will not offer that information unless you ask. "Aftermarket" Opti's, are selling as low as just under $200 now at the local national retailers. Not worth it. Unless, as I said, you plan to sell the vehicle soon.
Point is though, I have spent well over what a new OEM Opti would have cost all those years ago. ...and I'm not even factoring in the cost of the anti-freeze. Most of my Opti's were in the $450 range.
I can truthfully say that with the aftermarket Opti's, I wouldn't trust my car to be driven any farther than I could walk. There is no joy in starting you car everyday and wondering if this is the day she dies.
Yes, I AM trying to scare you. I do not want you to suffer the misery of OptiSpark replacement every 6,000-10,000 miles like I have. Google around, I'm being truthful. There used to be "better than OEM" Opti's out there, no longer the case. Those companies lowered their standards and quality. Even reputable "performance" brands have greatly slipped in quality/reliability.
Your best choices are OEM Opti, or, conversion to LS1 style ignition.
Of course, if you do go the the aftermarket route, you'll soon be able to do Opti replacements in your sleep. You will become very proficient in the procedure and it won't even seem like such a chore. ...it'll soon enough be as routine as changing your tire. *trust me*.
Just to give you an idea how crap the aftermarket units are, AutoZone will sell you a complete Opti for *less* than they sell the Cap&Rotor. ...It amazes me to no end.