Auto Transmission can't find Reverse - sometimes

What is your question?

Just in the last couple of days - It's like Reverse is an extension of Park. Then it will be ok the next day. Also - when it wouldn't 'find' reverse earlier today, my son said he revved the engine (foot on brake) with the shifter in the reverse position and it went into gear. Fluid is red and full. Could this be an 'easy' one like linkage or solenoid?