The computer is supposed to go open loop at WOT. What is the a/f during normal part-throttle cruise and what are the fuel trims doing? Is it in closed loop at part-throttle cruise? To me, it sounds like the computer is correcting a general lean mixture in closed loop, then when it gets to WOT and goes open loop, the base fuel calculation is off, possibly because of some of the modifications to the engine.

What do you use to read the real-time data?