I have a 91wrangler that has an auto that is having issues shifting going down the road when I get on it it will over rev but if I am doing more than 15 and put it in 2nd  there is nothing it is like it is in neutral.  but there is a 2nd when starting out but does not shift well into drive.   help what can I do.   and wil a tj auto fit w/ little problems??  

Sounds like the thing is shot. You have some sort of serious problem inside your trans. It could be caused by a couple of differant things but in my experiance once it starts slipping things get fried. Your second gear clutch pack is most likley gone and that is why it lets go and revs up when it trys to shift. Sorry for the bad news.