Hi,
The recommended source impedance for the ADC on the 45K22 is 3k, you have 30k - that might play a role in your results (see table 27-22 in the datasheet).

Since you have the acquisition time set to manual and such large source impedance perhaps you could try increasing the Pause 5 and see if that helps (or try reducing your source impedance to meet the recommended value of 3k). I'd probably also disconnect the signal from the second PIC until you get stable readings on the firts one.

/Henrik.