The mistake you’re making is that you’re coming into your Crucial Conversation unprepared. You’re coming in with stories, conclusions, and judgments but little or no fact. So is he. If the conversation sounds like…
Him: “I’m an excellent worker, a top performer and deserve a promotion!”
You: “I agree that you do good work sometimes, but you’re inconsistent and often disappear.”
Him: “No, I don’t! I’m always available and keep all my commitments!”
You: “Actually, you don’t.”
... then you're stuck in the “competing conclusions” trap. The only way to break this argument over vague generalities is to back up and start over. This time, with facts.