The trans. stays reverse no matter what gear you put it in

It is low on gear oil. When it gets hot it freezes up. Add gear oil.

yes it does sound like your Torque Converter

Does it have a automatic or manuel trans? You said gears, manuel trans, possible shift fork, syncro, anyway you will need
some serious work done to it....rebuild it or replace it.....

Sounds like an internal problem with the transmission which will take a shop to repair.

Often, it mean that the clutch stay engage.
Now the question can be, is the idle to high for the clutch to disengage while at idle? you might try to reduce the idle speed by turning eather the nob on carburator or the ajustement on the cable.

then if the idle is very low and the clutch still engage (that is why you can not shift) you migh want to check at the clutch and see if it is not stuck.

how many miles on it? how does the clutch pedal feel? how old is the clutch?

Put the vehicle in Park, disconnect the shifter from the shift lever on the trans, adjust the linkage or cable so the connection is clearly a slip in/on connection and tighten things back up. Hopefully this will solve your non-reverse. As for all the gunk and metal shavings, friend, you better have another tranny standing by in your garage when this one stops working completely.

Can you explain the shifting problem you are experiencing? Is it a slam into reverse and/or forward gears? Is there any slipping in forward gears?

The idle may be due to a dirty Idle Air Control (IAC) valve or a faulty Throttle Position Sensor (TPS). The first step is to remove the throttle body and clean it with some carb cleaner and get the black carbon off of the IAC and the underside of the throttle plate.

What was the code for the trans? Was it is incorrect gear ratio code or a vehicle speed sensor code?

The late shifting could be a control problem but the no reverse is not. These trans had a habit of stripping out the reverse sun shell, the metal from it may have gotten into the valve body causing the late shifting, but it really does not matter. If you have forward movement, but no reverse it has to come out. Sorry dude. You need a trans.

the trans needs to come out and be rebuilt