240 EFI Gen 2 SJ - Keeps fouling plugs

[240EFIGen2]

Hey all! New to this forum and hope you all can possibly save me. We have a 2002 240 EFI Gen 2 engine that keeps fouling plugs...like every trip out. This is a newer rebuilt engine from a reputable dealer that was put in last season. We have changed sensors, checked TPS, changed coils, etc... and almost every other thing that we can think of. The pictures below are of the port side bottom plug after only a 9 mile trip at 5000 RPM. The bottom 2 cylinders seem to always be darker than the rest. The black will not rub off at all. It's almost like it's been burnt on or dyed that color. We are at a lose. What would cause plugs to turn black and foul only after 20 mins at 5000 RPMs? Any assistance or direction is much appreciated. Thank you!