[A26B]

You probably have weak spark on 1 or more cylinders. It can occur on a single cylinder. The weak spark condition is not noticed during low RPM driving but will be noticeable under load as a misfire. It is most likely a coil, not plug wires.

There are 2 simple tests to determine if this is the case. I suggest conducting both to verify and isolate the cylinder(s) affected.

1. Load test in 6th gear at 35-40 mph, lug the engine. When you accelerate, not pedal to the floor, but 1/4 to 1/2 pedal, it chugs. If all is right, the LT5 will accelerate smoothly during this test.

2. Best done in shade or low light. Test spark by pulling one wire, attach a spare spark plug & lay it on the plenum to ground. Start the engine, hold the boot & observe the spark as you raise the plug. You should see a 1/2" long bright blue spark. An orange spark denotes weak spark. Repeat for all cylinders.

There are a few reasons for a single cylinder weak spark. The solution is to replace the coil. Your option whether to replace one or all four.

When replacing the coil(s), I recommend cleaning all the spade contacts on the coil base. Apply a light coat of dielectric silicone grease to the contacts before installing coils. Likewise, lightly lube the coil terminals & inside the wire boots.