I was thinking TM too. But can't remember it ever acting this way? Lag, lean then rich?

Can't really think of anything tune related that could do this if VE is dialed in, especially MAP and MAF?

What happens, or happened... if you were running Open Loop?

Bummer on the piston, but I don't think a 15 AFR lean spike during WOT caused it... unless it was some spark knock not being handled properly for a long time? Have you pulled the plugs and looked for specks/fly turds on the plugs?