96 850T AT-322 Gear 2 Ratio out of spec

[Texas Tea]

Last week while driving on the freeway my car stalled and the orange flashing lights came on. Geico towed the car home and the next morning only the CEL was on. The Volvo dealership spent 1.5 hours checking it out and said that the engine is in good condition but we need a new transmission. The only code was AT-322 and the ATF smelled burnt but is clean (it's Amsoil).

Prior to this incident the car has been running great except we don't have Reverse. But Reverse has been gone for 6 years (don't laugh ) We lost reverse after a mechanic did a trans flush. The other item is in Jan. the radiator was replaced with one from O'Reilly's.

Here are my questions: 1. Is it possible that this non-OEM radiator is not cooling the ATF well enough?
2. Should we install an auxiliary oil cooler and if so, which one?
3. Would you recommend any kind of cleaning of the transmission (torque converter, etc)? There's a place in Waco, TX that can do this that we trust.
4. Could the filter screen be clogged and how much time does it take to get inside the tranny to the pump suction line? Is it possible that we could also fix the Reverse so that it will grab?

Thanks for all of you assistance!