Use the AN number in ADCIN statements instead of the PORT.pin.

Code:
adcin 3,reading
And you don't need the ADCON0, VRCON or CMCON0 statements.
But you will need ADCON0.7 = 1 ; Right Justify A/D result

Since you are getting 1023 as the result, I assume you've set the ADC defines to 10-bit.

Also, make sure your primary oscillator is set to _INTRC_OSC_NOCLKOUT in the configs (it's the default).