That is true, it's only $8 at the auto part stores for 15 inch ground straps, and I'll need 2.If you don't have good ground engine-body and body-frame (and thus engine-frame), there may be tramp currents in strange places, and attendant voltage offsets (V=IR) between different "grounds" on the vehicle.
Ground wires are every bit as important as "power" wires, even more-so because grounds often provide a shared current path for multiple devices... which means, if the ground is bad, some devices can cause effects on others for mysterious reasons.
Can you tell me this: What's the return path for the current from the coil to the spark plugs? Remember, it has to get back to coil, somehow. Think about it.
Fix the grounds!
For $16 and an hour of work its worth it. Even if it's not the "problem" it may prevent further problems.
The return path for the coil to the spark plugs probably isn't great right now. Lol...