Have you checked the trans cooler portion of the radiator? Most radiators have a separate section that is designed to cool the trans. Trans fluid enters radiator, exits, then heads to external cooler, exits external cooler, and then returns back to trans. Basically, external cooler is added in line of trans return line.
My trans was heating up in hot weather. I pulled the trans return line and started engine to see if fluid was returning at proper amounts. It was not. I check to see if trans fluid was exiting trans at proper amounts. It was.
Therefore, the trans cooler portion was clogged. Again, this section or radiator is separate from engine cooling section. I replaced radiator and temps dropped considerably.
1992 Ford F-350 XLT, Crew Cab, Longbed, 4X2, 7.5L, E40D, 3.55, Tru-Cool Max Trans cooler
1998 Jayco Eagle 243RKS
Anderson Ultimate 5th Wheel Hitch
2014 Gregor Eagle Center Console, Mercury 60HP 4 Stroke, Garmin 93SV FF, Motorguide Xi5 GPS