Overheating 360 new engine

I don't know if any of these have been mentioned yet, but here goes.

Serpentine belt setup- is it turning the water pump backwards from normal? Magnum engine serpentine belt set up does is why I ask. Maybe this one does as well? If so, a flowcooler water pump that has a round disc covering the impeller blade could be the answer.

Also, if the distance between the impeller and the water pump housing is not right it can cause cavitation and cooling issues. This is becoming more common with the garbage stuff for some aftermarket parts. Disc on the impeller can help with this as well.

As far as the fans go, you should not need any fan of any kind to keep things cool at a constant 55mph on the highway. If yours is overheating at speed you have another issue than just the fans.

Fans could still be a problem in stop and go traffic though. As someone mentioned earlier a full shroud surrounding the fans and back side of the radiator is likely needed.

Is your aftermarket radiator a tight fit around the edges to the core support? If there are big air gaps around it air may not be flowing through the radiator and instead going around it. Some weatherstripping can correct it if so.

Hope this helps.