Have you checked continuity between pins A & E at the plug goint to the NSS with the selector in reverse.
If you have no continuity, then it is the NSS at fault & time to rebuild. Easy to check witha multi meter. Select Ohms, then short out the multimeter probes to see what a zero ohms or continuity reading gives you. Now place the probes onto the pins.You should see the same reading or similar for continuity. If you have continuity then go to the other side of the plug and select the same pins and do the same test.
http://www.cherokee-jeep.com/1-2swremov.htm
Just saw your update. You may still need to do the refurbish to eliminate the intermittent fault.