Looks like we nailed it!
Thanks guys. This is why I love this forum.
Tonight, I installed my new Walbro 255 Lph fuel pump and took it for another test drive. Before the pump, my fuel pressure at idle was 61 psi and by 5,500 at WOT it dropped down to 38 PSI. It was even lower before changing the fuel filter, but I did not record it. More importantly, at WOT above 5,500, the AFR jumped to 20:1 (extremely lean).
After installing the new pump, the idle pressure is 68 PSI and under max load at WOT, it never drops below 60 PSI. The AFR is now at the opposite extreme. At WOT at 5,500, it is way rich at 10.8:1. This means the lean issue is absolutely fixed by the fuel pump. Now it is running rich because it was originally tuned by BEGi with the OEM fuel pump with lower pressure. It was dark outside, so I could not see if it was putting out black smoke from running that rich. I'm guessing it is.
I have another question.
Before the fuel pump failed, the AFR was in the 12-13 range at max WOT max load. What are the side effects of running this rich (10:1) at WOT? Is is just low fuel efficiency, black smoke, slightly reduced power, and more likely to foul plugs sooner?
Thanks again guys for the help. Looks like my TWS weekend is going to happen. It is not nearly as much fun to instruct when you don't have your car to go play.