The above responses cover the subject pretty well I think.
Yes, torque redline is normally the gearbox limit, and is more likely to be reached at low altitude/low OAT because of the increased air density and engine mass airflow, thus more physical HP.
And turbine temp (TGT, ITT, ...) is more like to be reached at higher OAT and/or altitude. It's an engine limitation, unrelated to the gearbox.