I have a 2000 Nissan frontier 2wd. It won't back up and doesn't have neutral when running but does when it's off. Any help would be greatly appreciated. Thank you.

If the light was on you could have a bad solenoid in the valve body the codes would need to be inspected , but from what you have described it sounds like a mechanical failure inside the transmission, with the low and reverse stuck in low gear , to fix that type of problem the transmission will need to be torn down or replaced the transmission to fix the problem you are having. Don't take it to Performance Transmission.

Performance Plus Transmissions Washington Rd can fix it by completely rebuilding the transmission an have,it done within 3days, with a 1year or 12000 mile Warranty which ever comes first.