Most agree that air flow is the issue. Having been in this position before, I'll offer a suggestion that has worked for me; I go to a pick-a-part yard and pull a fan from an 80s Dodge pick up. It is too large in diameter to fit in the shroud. But, it's aluminum so it's easy to cut down, is lighter than the steel fan you have now, and it's balance isn't hurt much with the trimming.

Those fans move a LOT of air. More blades and more pitch to boot so it gets a clutch due to the additional drag. I have used this on several Mopars with no down side. Currently I have one on the 540 Hemi in my Cuda and it still has the original re-cored radiator with a good shroud.

And, if it matters, this route is cheap.