The V8 runs cooler than the V6 (witness the radiator cap pressure ratings for each), so the switch on point may be too high for the V8 if it is the same in both. What I would like to see if setting up a V8 to run thermo fans would be the normal operating temps under a variety of conditions, with a factory set up, and then match that by setting the thermo fan switch on point or points. Access to a datalogger would help in this; a cable and Winaldl (or similar) would do.
having just checked the standard trident thermostats,
V6 = 195degrees F (90.6 degrees C)
V8 = 190degrees F (87.8 degrees C)
optional cooler thermostat, 180degrees F (82 degrees C)
have just checked the standard settings
V6
on temp = 101.75 degrees C
off temp = 98.75 degrees C
V8
on temp = 107 degrees C
off temp = 101 degrees C
VN-VR only run single speed thermo fan although there is provision in the tune for 2 fan settings (2 speed thermo's) however there is no extra wiring in the loom that i am aware off to use this extra function
VS onwards do use a 2 speed thermo fan setup on the V6 (unsure about the V8 models as i haven't really ever looked at there wiring diagrams to compare to the V6 wiring loom)
so if you were to use the factory circuit from the ECM you would either want to have the memcal altered to switch on at lower temps or use an aftermarket controller.
no doubt Dr bob would alter a memcal to suit for a small fee but then why not spend a little extra and get a tune done by Dr bob also