Not sure if you figured this out, but 10bit AD need to be read out as RIGHT justified, and 8 bit reads should be LEFT justified. Here's a config that works for 8-bit:
ADCON0.0 = 1 ' AD ON
ANSELA = %00000001 ' select analog vs digital (1=analog)
ADCON1.7 = 1 ' bit7 = 1 = LEFT justified
define adc_bits 8 ' set ADC as 8 bit