PIC18F2620 Internal Clock Jitter
SOLVED. The problem was the power decoupling of the PIC18F2620 device. I changed the 0.1uF to a larger 1.0uf and then placed an additional smaller 0.01uf in parallel with the first. The 1.0uF intended as a "power resevoir" and the 0.01uF as a noise filter. This configuration cleared up the jitter problem nicely.
Thanks to all who posted hints and answers.