The car will automatically reduce power output when it gets hot. If you're tracking the car it doesn't take long for this to happen unless some things are tweaked in the tune.
Of course without seeing a datalog I would only be guessing.
If you can't datalog, the next thing I would try and...
I would reach out to Counterspace garage, they are in Cali and are actually in NorCal now working on customer cars.
They've also have shown really nice power gains when using or Flex Fuel Kit on the Supra
All the ECU's are "locked", the dealer flash update simply blocks the .way we get into the ecu, preventing us from unlocking OBD Programming for non-OEM tunes.
If your ECU gets updated it will have the latest update which no one knows how to OBD Unlock.
This is where our unlock services comes...
When the car comes in for service they aren't looking to see if it's tuned, they are just checking if it has the latest update.
They will most likely flash over it.
If they do we can unlock the ECU to work with BM3 again, or switch to EcuTek