GPS is your strongest evidence, and it says less than the argument claims. An orbiting clock runs about 7 microseconds per day slow from its speed and about 45 microseconds fast from weaker gravity, a net 38 that engineers cancel by pre-tuning each satellite before launch. That number is real and unarguable. What the correction actually requires is the metric. The block universe is a reading placed on top of it. Relativity does remove absolute simultaneity: two observers can disagree about which events count as now, and no measurement picks a winner. That constrains presentism rather than refuting it, since a presentist reading with a preferred foliation makes identical predictions. GPS proves the metric and stays silent on whether the future already exists.