[scarceller]

I went through all the posts in this thread again today. The AFR city graphs clearly show you are in the correct target 1.0 lambda and you do not have black plugs nor black tailpipe. These 3 things tell us you are not running rich.

I'm not sure what the issue is here but it's most likely something mechanical. Double check all ignition components and firing order.

Also 27-28MPG highway is on target and as expected.

Some sort of extra mechanical drag is what I suspect, but not sure what that is. Could be collapsed brake hoses? Are these new? Test is easy to do, car on jack stand. Engine at idle in neutral. Have someone apply the brakes and attempt to turn a wheel by hand. Then have them remove foot from brake pedal. The MOMENT they lift off pedal the wheel MUST spin easily. If you find a delay between time they took foot off brake and wheel spins you have a bad hose.