Most likely it is the NSS. Have someone see if the reverse lights act goofy, the NSS also controls when they come on.
Take it off and apart, clean up the contacts, reinstall. I've done this before, hardest part is getting it off. Be careful, its just plastic. Looky here...http://www.jpmagazine.com/techarticles/drivetrain/154_0805_1987_2001_jeep_cherokee_neutral_safety_switch/index.html
