In this article regarding Lambda ECU's it is mentions there is a well known "Pulling" effect while constant driving/cruising. I haven't been able to find any more information on this well know effect, however it does seem to resemble the issue I am seeing. Anyone know more about this?
https://nineelevenheaven.wordpress.com/optimized-control-unit-ecu-for-the-911-sc-with-lambda-control/