Summary of Problems for the GPS
1. GPS satellites clocks run slow by 6 millionths of a second per day (SR - time dilation)
2. Cannot synchronise by exchange of signals
3. GPS satellite clocks run fast by 45 millionths of a second per day (GR - gravitational blue shift)
Net effect: Run fast by 39 millionths of a second per day (12 kilometres)!
SOLUTION: Make the clocks run slow to compensate!