Had the exact same problem with my Demon and the 5.9 Magnum. Two core aluminum rad with two electric fans and an aluminum shroud. The engine ran at ~180 in town and 215 on the highway. After a year I took the shroud/fans off (just last weekend) and bolted on a 18" fan with no clutch. The fan sits about 1.5" back from the radiator and has no shroud. It now runs ~180 in town and ~195 on the highway in 100 degree heat.

BTW, Feets was the one that turned me on to this fix.