Transmission problem ???

My 92 teg just got a rebuilt motor installed. This problem happened before the rebuilt motor was installed.
The problem is when I slow down to make a turn or slow down and then
accelerate again, the car always jerks forward or does not transition from slow to fast smoothly. I think this is my transmission problem but I just wanted to check if it could be anything else that could be "less expensive" to try to fix first before spending lots of money.
Any ideas would be appreciated.
Thanx.
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Did a little more research and I found something I can try is to clean out the transmission vacuum modulator. But where the heck is this modulator located on a 92 Teg? Is it easy to replace?

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