A dirty MAF can cause that also. Look for dark film on the air filter side of the small sensor wires (requires a Torx tamper-resistant bit to remove sensor). Clean with brake cleaner and compressed air. Might want to check/clean it first before you start buying parts.
make sure you dont have a plug wire grounding out. It would still be missing but at crusiing speed you "might" not notice it. Tonight when its dark open the hood and start the truck and look for sparks. Or with the engine off just look for burnt areas on the plug wires. could be a place to start looking.