Check engine light after front seal replacement

I had a new transmission put in at 75,000 miles. One year and 15,000 miles later my front seal was leaking. Took in back to the same place. They replaced the front seal and the torque converter. Ever since then, the check engine light comes on after 45 minutes of driving in the mountains. The transmission seems to be working fine. The light tells them it is overheating. The put a new selenoid pack in and I am still having the same check engine light problem.
Anyone have any thoughts on this?
Thanks

Usually for a computer to read an overheating condition there must be a sensor somewhere. I would have the trans temp sensor checked or replaced. It shouldn't cost a lot and if the transmission is still under warranty the transmission shop should cover the cost.