A760F issues.

Last summer I had driven my Tundra (170k miles) down to Texas from WV. During said time I was running the truck back and forth from San Antonio to Austin where the temps on the dash were reading 110F to 114F outside. Well on one of the trips I had a transmission overheating warning pop up on the dash and started getting slipping in 6th. Pulled over and let it cool for a while, when I resumed my trip I locked it into S4 and took it easy. Took the truck to a dealership out there, they said they couldn't replicate the issue.

When I got back home to WV, I took the truck into the dealership, asked for a drain and fill to get rid of the cooked fluid.

About a month down the line I lost 5th and 6th completely (P2714 DTC). When looking through the service history to see if the previous owner ever had serviced the fluid I stumbled upon my last service and read further into what they performed... A BG Fluid exchange, which to my knowledge is a flush... Now Toyota is saying I need a new transmission.

I've swapped both input and output revolution sensors on the transmission, performed my own fluid level check (within spec).

My questions are:
Could that flush have clogged the valve body, thus just needing cleaning?
Could that flush have caused said clog making Toyota responsible?
Is Toyota just throwing the parts cannon at it recommending an entire new transmission based on one DTC?

I'm at a loss here... One is either labor cost at a transmission shop, the other is about $6500....