Territory Transmission Issues

Sounds like the transmission oil temperature sensor is faulty. Do you know if the error memory contains a fault code? I had a similar experience with my Territory (though it's a newer model). What's the gearbox oil level?

Oil level... hadn't thought to check that. But if it's just the sensor, why is the gearbox acting like a coffee grinder? Is it really possible that a faulty sensor can cause all these problems, or is that just the tip of the iceberg?

The faulty sensor can trigger all those symptoms. The transmission goes into emergency mode to protect itself, which leads to the rough shifting and grinding noises. The most probable cause is a gearbox oil level too low in conjunction with the faulty sensor. Either way, it’s probably best to visit a workshop. They can read the fault codes and check the oil level. Trying to drive it like this could cause even more damage.

You were spot on! Took it to the workshop, and they confirmed it: faulty transmission oil temperature sensor and low oil. They replaced the sensor, topped up the oil, and now it's running like new! Cost me 365€, but well worth it. Thanks for pointing me in the right direction; I really appreciate it!