GP3 Funtion on PIC10f202

[kessral]

Hi all,
I am having problems getting GP3 to function as input only in a PIC10f202. Just for testing purposes I am trying to very simply blink and LED once per second on GP0 and throw in an extra pulse (pulse twice per second) when GP3 reads a low on input.

Here is my code:

trisio.3 = 0
loop:

high gpio.0
pause 100
low gpio.0
pause 500

if gpio.3 = 0 then
	high gpio.0
	pause 100
	low gpio.0
endif

pause 500

goto loop

It is currently pulsing twice per second, and the chip ceases to work when I make GP3 low by pulling it down to ground.

I am using MPLAB IDE v7.11

Are there any obvious settings I have missed?