So, you are driving down a flat road at say, 55 mph, and cruise control is on, you are showing a constant 5° KR? Only thing I can think is that the overkill tune ramped your cruise timing for better mpg, and your car is not liking it. Being lean doesn't help, but you are not so lean that it should matter under stock timing.

Your options seem to be: 1 get in touch with OK, 2 get in touch with OK, 3 pulley up.