AFR slowly richens at idle

Too much cam

Drop in your cam Lift, Duration, Duration at .050 ths, and lobe center numbers here so we can see where your cam operating rpm numbers fall into.

Guessing you have a cam that operates in the 2000 to 7000 rpm range.

A cam in the 1000 to 6000 rpm operating range would be a lot easier to get a better idle out of for street driving applications.