Inconsisten movement speed of the viewport

[Jeff]

Are there any framerate drops when collision is enabled? Even an occasional drop may affect your calculations. I took a look at your example. I would suggest that you simplify that to the minimum code possible, perhaps just have forward movement in manual mode. I'm not immediately able to see from the log file what the speed or error is. Unless you don't want to publicly post your model, it's best to post everything here so other users can help as well.