Trans won't shift

Recently acquired 92 735 IL will not shift out of 3rd when in Drive. Car has 114K miles is in fair condition and don't know of it's history. A repair shop recommended a new transmission for $2,400, I would think is could be repaired but what do I know ! Will be greatful for any help. Bedford

have you checked to see if the trans is stuck in sport mode?
sport mode will lock out fourth gear.

mark