I've never run into a ground problem but I read about them quite often. At this point I have to defer to my Chrysler experience. GM and Chrysler do a lot of things the same way. There are four ground wires on their Engine Computers. Two are "power" grounds and two are "signal" grounds. Power grounds refer to things that use high power, typically injectors, ignition coils, relays, and solenoids. A very tiny amount of resistance due to corrosion in the power ground wires will result in a small voltage drop. Those little voltages, which are pulsing and intermittent, would affect the sensors' signal voltages, and that can mean a huge difference to the computer, so those ground voltages have to be avoided. That's why the sensors have their own dedicated ground wires.
Both systems have two ground wires so one will handle the job if the other one has excessive resistance. For that reason, it isn't common to find ground problems with the Engine Computer.
I suspect the leds on your scanner are simply saying the readings from the oxygen sensor can't be trusted, and the catalytic converter is going to be damaged if the defective condition is allowed to continue.
The first thing to suspect with any code 300, random misfires, is worn spark plugs and wires. Most of the time that causes a single-cylinder misfire with the affected cylinder being identified by the code. Since yours aren't that old, the next thing to consider on high-mileage GM vehicles is the injectors. Chrysler, and I assume, other manufacturers, buy their injectors in flow-matched sets. GM grabs a handful of injectors from a big bin and throws them into an engine with no regard to matching their flow rates. That doesn't cause a problem at first, but with high-mileage wear and deposit buildup, one or two will start to flow less fuel than the rest. A lean cylinder will result in excessive unburned oxygen going into the exhaust where it will be detected, and the computer will respond by adding more fuel to that side of the engine. Most of the time that doesn't result in a misfire you can feel. It results in excessive fuel consumption and emissions.
Instead of ground wires, a better place to start is another common problem that only affects GM vehicles. Due to their design, their generators starting with 1987 models develop huge voltage spikes that can interfere with computer sensor signals. That is a common cause of elusive random misfires that defy diagnosis. Those spikes also destroy the generator's internal diodes and voltage regulator. Where I would start is by having the charging system tested for output current and "ripple" voltage. With one bad diode of the six, you will only be able to get exactly one third of the generator's rated current, and ripple voltage will be very high. If the generator is found to be defective, to prevent numerous repeat failures, it is important to replace the battery at the same time unless it is less than about two years old. The battery is the key component in damping and absorbing those voltage spikes, but they lose their ability to do that as they age.
Sunday, February 22nd, 2015 AT 6:00 PM