Why am I exhausted when every project I run succeeds?

You say you can run any engagement to impact. That's a skill, not a life sentence. But you talk about your days as "measured in billable travel," as if someone else holds the measuring stick. No one hands you that stick. You picked it up, or let it be handed to you, and you can put it down. The exhaustion is real. But ask yourself plainly: is it the flights wearing you down, or the fact that you haven't decided what any of it is for? A string of wins with no aim behind them tires a man faster than any travel schedule ever could. You don't need a sabbatical or a new system to fix this. You need to decide, today, which engagements are worth you and which aren't — and act on that decision this week, not someday when things calm down. They won't calm down on their own.