Random lean spikes after letting off throttle

[ferocity02]

I installed a 4L80E and a new converter and noticed an issue on the highway. Sometimes when I let off the throttle I will get a very lean spike, almost like the engine it trying to die, but it will catch itself. Sometimes it happens many times in a row. It is more common after some medium-heavy throttle.

Fuel pressure looks good, but the IBPW drops very low causing the lean spike. And ideas where to look in the tune for a cause?

I had a T56 before and it never did this.