Over heating on the freeway?

Im so Confused...My stock dart, 273 2bbl , no shroud (factory) stock fan inches from face of radiator (factory), correct thermostat, stock radiator, average water pump, no overheating issues.

410 CID
1 " single cross row BMW radiator
18" fan
No shroud
8 blade stock water pump
Exh cross over blocked
High flow 180 t stat
16lb release rad cap
10.1 static comp
8.88 dynamic comp
Pump gas
Never overheats.