Trans temperature gauge

I have a F150 (7700 series) with 4R100. Extra oil oiler and temperature gauge in the oil line going into the rad. Oil temperature in winter never goes about 100° unless I'm in town. In the summer it runns about 140-150°F pulling our 24 ft 5th wheel. Only time I have seen it go 170 or higher was stop and go traffic or parking or going up a couple of grade in the White Mountains in July. The temperature will go back down the minute the torque locks up. Their is a temperature bypass in the $R60 and 100 that will not allow it into OD unless the tranny is at operating temperature.