Dodge transmission fluid

I went to top off my tranny fluid the other day (97 Dakota) and noticed the manual calls for ATF+2 specification fluid. I think Walmart only carries generic transmission fluid so I went to OReilly and sure enough they had a couple of different kinds including ATF+4 (supercedes ATF+2). So is there really any difference between ATF+2 and just regular old transmission fluid? I assume it's a marketing ploy so you'll spend more money. I remember in the 'old' days (60's-70's) there was type F for Ford, etc. Even back then I couldn't figure out why there was or needed to be a difference.