I wonder if that rich dip in your fuel curve is due to overlap of the transition circuit and the main. At 3500 the motor may be pulling decent amount of fuel thru the mains while the transition is still flowing a noticeable amount. Above that point, the transition may be flowing less and the mains more. Leaning the main jet will cause your 4K RPM to be leaner as well, and some care may be needed to balance between getting it perfect at 3.5K and having it too lean above that. The main jet change will obviously lean up the WOT AFR as well.
Sometime back I realized my motor is also pulling fuel thru the mains at 3K cruise, contrary to my original thoughts. If I went really lean on the mains, the 3K cruise AFR can be improved. Geting the right balance is going to be some work though. However, last weekend I pulled the intake again, and confirmed I am still getting oil into the runners, so I need to resolve that before tinkering any more.
I'm glad you are back in business with the wideband. Your motor seems like it is running like a fine clock. My wideband has been fine so far, but I'm lacking on the motor side. Hopefully soon we will have both motor and wideband working well at the same time!
