My cousin recently bought a 2000 GMC Yukon with the 6.0L engine. After running the engine for about 30 minutes, the computer throws codes P0351-P0358. It looks like they're codes for circuit malfunctions on all 8 cylinders. The engine runs fine and doesn't seem to misfire or anything. The previous owner said he changed the coils and my cousin has already changed the plugs and wires. There was predictably no change. Logic says the issue shares some commonality since it's all 8 coils and each coil fires 1 cylinder. Commonalities I see are the grounds, the hot fuse, and the computer. Even the signals from the computer to the coils take 2 different bulkhead connectors to get to each bank of coils. Any ideas?