From what I have seen, when this happens the transmission clutches inside are damaged and you will need a transmission overhaul or replacement of the transmission, reverse band and clutches bad. Thanks let me know if you have more questions, ROY!
This a common problem on the pathfinders the clutches go bad I would tear it down in spect clutches and seals for leaks inside . Thanks ROY!
I would get a manual to help no special tools straight foward , I will be off line until tomarrow if you need more help , Thanks and good luck ROY!
Thank you and good luck , ROY!