Crazy drop shifting when letting off the gas?

[rahmat8303]

hello everyone... I'm new here but I've been searching up and down for a solution to my problem for a while now especially here.

Problem:

I have an '89 automatic 240sx which idles great. Everything sounds wonderful. However, when I'm driving at any speed above 30mph, when I let off the gas, my transmission violently down shifts and the revs jump between 500-1000rpm depending on my speed (higher speeds=higher revs). It feels like it's downshifting from whatever gear I'm in to 2nd gear but I'm not sure. There aren't any problems when I'm in 1st or 2nd gear driving slowly. I've already had to replace the transmission cause something inside snapped due to the down shifting and I've also tried replacing the TPS which helped smooth out the down shifting a little, but it still does it. Every mechanic I've taken it to has no idea what the problem is.

Please help 'cause I'm at a loss.