The two boxes I'm almost certain are completely different

But obviously work on the same principal.
Your torque converter is separate to your gearbox. It's the part that goes between the engine and gearbox.
It looks like a very fat flywheel and it's full of oil
This is the part that transfers the engine power to the gearbox.
We can test it, if it's still in the vehicle and you have a rev counter connected to your engine.
This is what is called a stall test;
Engine must be warm to carry out test.
Chock all wheels of the vehicle to prevent vehicle from running away.
Make sure hand brake is applied.
With the foot brake applied, engage 'D'.
Press accelerator to the floor for NO MORE THAN 4 or 5 SECONDS MAX***.
Make a note of maximum revs via the rev counter.
If your revs didn't go above 1000rpm the you have stator slip and you need to replace your torque converter only.
If your revs went high eg; say over **2200rpm your gearbox is slipping and this will need to either be seen to or replaced.
**This reading will be governed by what type of torque converter is fitted.
By this I mean you could have a 'high stall' converter or a 'low stall' converter.
You may want to replace your torque converter any way just to increase your take off at traffic lights

but this would have a penalty to your fuel consumption
***This test generates untold amounts of heat and prolonged testing will cause damage to both the engine and transmission assembly. Allow a cooling period if you need to retest
I hope all of this helps a bit
