lol craigslist tranny! let think about this if you buy it and it locks up or mulfunctions you might need new engine.
like i said tv cable does not help, try tps and let me know if it helps. i did the tv cable adjustment computer reset, transmission flush and took it in to aamco here down south in fl. and they go no clue what it is. your best bet is get a new tranny, as long its not from craigslist.
like i said you can get new one put it for 3k at the shop, they got decent ones on ebay, but once again not sure about are they build right.
luck all keep me posted if you find a solution gotta get my r/t running

 

I wouldnt worry about craigslist trannys just get it looked at before you throw it in. Actually the one in my 95 woods beater has a junk yard tranny in it and 80k later still alright. I've also had a tranny lock up on me and did no damage other than to itself at 50mph

 

Try checking the speed sensor to see if it is functioning correctly.

There are businesses that take engines and transmission from junkyards and rebuild then sell them, it just all depends on who is doing the rebuilds.