overheating issue

First thing Air Bubble
Next Not enough radiator rows
Next Is it really overheating?
Next Is radiator cap pressurized?
Last Motor timing

It can also be an interesting dynamic of running hot at low speed because of the fan and running hot at speed because of no airdam under the car.

Good luck.

Couple of things I can think of:

Air Bubble as stated by CorvetteGuy, Take the radiator cap off, jack up the front drivers side only and let run until reaches operating temp, see if radiator burps out air and fluid drops.

Thermostat installed backwards? Is the nipple facing out towards the front of the engine?

Black Magic fans have a bad rep for inadaquate air flow for our engines stock, much less modified.

Is the fan pulling air and not pushing? Fan could be wired backwards making it a pusher instead of a puller which would cause an overheating issue.

With the fan being wired for constant on, this could causing your overheating at speed, the rotating fan blades can cause more of an air restriction at speed.

Lack of a lower air dam as stated by Hissin.

Thats all I can think of right now.