transmission issues

I have a 2003 V6 Jeep Grand Cherokee Laredo with Auto transmission. Every once in a while, the transmission seems to slip while in a low gear (2-3 times a month) - it almost seems as though it is in neutral, revs really high when I try to accelerate, and eventually (but slowly) accelerates. This generally goes away when I stop, put it in park, and attempt after several times to put it back in drive. I also noticed that it accelerates (when operating "normally") slowly, and seems to hesitate changing gears in lower gears, kinda like its jumping back in forth - its almost as though a gear is missing, I'm not sure if its 1rst or 2nd, but it isn't entirely obvious as though a gear is missing altogether. There is also a "whining" noise when it revs high when it does accelerate. Thanks!