2006 ford f250 diesel Transmission over heats

What is your question?

We have installed a new transmission new radiator new trans cooler. Replaced everything. We can drive for about 30 miles on the highway when the trans temp will start to climb with in two miles the trans is over heated. We have verified the trans temp not just trusting the gauge. We let it sit for 20 min. and can go another 30 miles before it does it again. Checked to make sure exhaust was not a factor. All the lines are clear no bends or restrictions. If anyone has any Ideas Please help.

What makes this problem better or worse?

Normal driving no load

How long has your 2006 Ford F-250 Super Duty had this problem?

I have been working on this for a week