[Monster]

It appears that you have not applied the suggestions from a number of folks that have been through this issue, that your issue is AIRFLOW and that your problem appears to be an issue with the design of the shroud that you previously had installed. (not pulleys, t-stat,timing etc.)

Shroud's are a critical component in cooling, just look at any modern car. Not installing one reduces the effectiveness of your cooling system (especially at low speeds)

From SPAL:
The efficiency of your cooling system depends on the following factors:
Radiator core size (the size of the radiator inside the tanks where the cooling tubes and fins are located.) This space determines the diameter of the fan.
Space required for a cooling fan. Our High Performance cooling fans require 3.5-4.5-inches in depth (from the radiator core to the fan motor cap). This distance may be shorter if the cooling fan can be offset on the Radiator to clear the water pump.
Radiator material and number of cores. An aluminum radiator is more efficient than a copper radiator.
If a shroud is utilized: For the most efficient system a shroud should be utilized. The shroud forces the fan to pull air across the entire radiator core area, opposed to a fan without a shroud that pulls air only across the diameter of the fan.

Currently, without a shroud, in traffic (lower speeds) you do not have sufficient airflow going through your radiator. Air is only being drawn through the area directly in front of your puller fan. The area of your radiator according to what you posted earlier is approx. 393.75sq.inches and you have an 16" fan (201sq.in) which calculates to approx. 51% coverage/draw through your radiator.

As Olddog, 767jockey and Brettco observed the design of your "old" shrould appears to be an issue (not allowing sufficient draw). By increasing the space between the shroud and radiator to a minimum 1" at the outside edges and tapering to 2" at the fan you will increase the draw through the entire radiator which will improve airflow/cooling at both low and high speeds.

Try this, what do you have to lose at this point.

good luck,
Mike