Hey guys, I was driving my 2000 Xterra 2wd Auto 3.3L the other day and when I went to make a 3 point turn reverse and wouldn't engage. I gave it some gas and nothing, I just sat there. I gave it some more gas and it finally engaged, chirping the tires and then allowing me to finish my turn. I parked it and when I came back today it did the same thing. It's also making a light grinding sound when I put in in park, I think it is trying to change gears but isnt' able to really do it. I'm pretty sure the tranny is shot, but I thought I'd ask you guys if you had any ideas. The car has 150K miles and I'm pretty sure it's the original unit.
Thanks in advance.

low fluid