If you're overheating while moving at more than 35 mph, you don't have a fan problem. Airflow due to vehicle motion at that speed is sufficient and adding a fan won't help the situation at all. You have some other problem that needs to be addressed. Auxiliary lights blocking the radiator opening are probably a significant contributor, but it sounds like you've got that handled. Is the plastic shield below the radiator in place and in good condition? You have a stack of heat exchangers (condenser, radiator, trans cooler) that you're trying to force air through, and the incoming air will take a path of less resistance if one exists.

You might want to experiment with running 100% distilled water along with Redline Water Wetter (or an equivalent product), and a higher pressure radiator cap.