How much initial timing is too much? Running hot on the highway.

Downtime! said
The shroud is not much of a shroud, more of a plate that covers the back of the radiator and provides a mounting point for the fans. There seems to be a pretty good flow of air when the fans are on.

The fans do relatively little at cruise; they cool at low speed and idle, and should be rated to remove lower engine heat output than is generated at cruise conditions. My concern is how you describe the shroud above. If it is a flat or fairly flat plate with holes in it the size of your fans, that is very probably the issue, and is blocking a significant potion of the needed air flow at cruise. Can you please post a pix of that shroud? The only pix where I can a small edge of the shroud looks like a rather normal one, not like you descibe above. Is there a flat plate shroud inside a plastic shroud?

I have jacked up the rear of a the hood on a race car; it helped, especialy when things got slow after running hard and getting a lot of heat in the manifolds, etc. But you need to resolve what is likley a shroud problem first.