ADC resolution for 16F616

I'm using a 16F616 analog input with a ADCIN routine. My resolution is 5V / 256 = about .19 mv. I'm using a voltage divider for the input with .1% tolerance resistors. Is there a better way to improve my accuracy? It seems that my code is not reacting to .19mv steps, more like 100 or 200 mv at best. I tried 10 bit resolution but never got that to work - pretty sure my code was wrong.


DEFINE ADC_BITS 8
DEFINE ADC_CLOCK 3
DEFINE ADC_SAMPLEUS 10