Just Rebuilt my Lt1 Reused Opit and the wires are less than a year old and new plugs. The only time the car will miss is if it's raining or the air is very damp. It only does it at cruise or less than 1/2 throttle the idle seems fine but it will throw a code if i let it sit and idle. Like i said it only does this if it's raining or if the air is real damp.

 

I had roughly the same symptoms with new plugs wires opti and coil, and mine turned out to be a cracked spark plug, watch the plugs as the cars running at night see if you have any light effects around the plugs wires or boots.