For GPS, in addition to the time-dilation effect due to relative speed of the satellites with respect to observers on Earth, there is a second, smaller (iirc) e

For GPS, in addition to the time-dilation effect due to relative speed of the satellites with respect to observers on Earth, there is a second, smaller (iirc) effect to take into account: that of the different position in a gravitational well, which is a purely GR effect.