they are related. the po725 code is a transmission code. it is because the transmission control module is not receiving an engine speed signal. the engine speed signal comes from the engine control module to the transmission control module. the engine control module calculates this speed from referencing the crank sensor.
your problem is all because of a failed crank sensor. replace the crank sensor and you should be fine.
also note, the new crank sensor you will be installing is different than the one you remove, Nissan has updated the part to a new improved sensor.
This is exactly what I was hoping to find out. What happens if I when I replace the crank sensor the engine light still comes on and I still have the performance problems? What would I do then?
one step at a time.
fix the problems you know you have. then we will work from there.