I read through that link you posted, and they put in 12-16 degrees of vacuum advance, bringing the total (initial plus centrifugal plus vacuum) at part throttle to 45-50 degrees. Maybe this could be causing an issue as my total without vacuum is only 36 degrees.

I also checked my fan clutch, and it is fully engaging. I stuck a rolled up newspaper into the blades and they didn't stop/slow down so the clutch is good. I may pull it out and adjust the spring so that it fully engages at a lower temp.

Another thing I wanted to bring up is gaps in my fan shroud. It does not fit perfectly to the aftermarket radiator and there is a gap where the shroud overhangs and inch or two. I has notched the shroud around the inlet for the transmission cooler, but I may need to notch it a bit more to sit flat.

The fan seems to be sitting in the shroud correctly and I attached a photo of that. Would it be of any benefit to move the fan closer to the radiator? A few guys I’ve talked to have mentioned trying that.