Then I am screwed if I have to stop or slow down. I have a 160° thermostat, 440 source water pump, mechanical fan, and no shroud. I will make a shroud prior to purchasing a radiator though.
The rule of thumb - if you overheat going slow or in traffic, it's an airflow problem. If you overheat at rpm on the highway, it's a capacity for heat rejection problem. Sounds like you're on the right track, a proper shroud might fix it.
