FWIW. My friend Jerry ran a transmission repair shop for 30 plus years. It was not uncommon that a customer came in and mentioned that after having their transmission "flushed" it began to have issues.
Drop the fluid and replace the filter is enough when servicing your transmission he advised.
Now, your issue was before you had it flushed but something to think about as we motor on down the roads......
Also, when climbing hills, turn off the AC. Heat generated by the AC contributes to increases in water and oil temperatures. Up front you have various coils for AC, transmission and then the big one, your water radiator. All competing to dissipate heat away from important stuff.
Best of luck getting your Rig back in service.
I carry a code scanner in my rig to help diagnose issues while on the road. Also many auto stores will scan free of charge. The scanner reads code ***. you look up code *** on internet and bam, you are more informed of your issue.