Sorry, I should have explained better.

The PIC IO pin is fine for driving the regulator ENable input... you shouldn't need any other circuitry. Set PORTB.2 as an output low to power off the GPS, and then set it high to turn on the GPS. Leave it as an output high, otherwise the regulator may shut itself off.

However, when you have the GPS power off you must make sure that NONE of the PIC output pins that connect to the GPS are high, otherwise the GPS could get partially powered from those logic lines that are sourcing 3.3V.

The UART TX output pin idles high once the UART is enabled (RCSTA2.SPEN, bit 7 = 1), which I think happens during initialization. With SPEN = 0 the uart TX and RX pins are under control of the ports.