1991LuminaDave

Hello I have a 91 Lumina 3.1 Sedanwith 104,000 original miles. Recently while driving the car will just randomly start shifting up and down while driving. I will have my foot on the gas going like 35mph and then the speedometer will jump to like 45mph to 15mph then to 45 mph again and then 15mph then back to normal. Then when coming to a stop i can hear the car engine very highly idling. Then I shut the car off and turn it on again and the high idling is gone. Recently in the past 3 months I have had the transmission rebuilt with new torque converter replaced because when coming to a stop the car would stall and then would start however would want to stall again unless the floored the car to keep it going. Also recently I had a vacuum hose replaced because the car kept stalling when coming to coming to a complete stop. Also around the time I had the vaccum host replaced which was last week the car when it was stalling would feel like it would want to jump forward when I was sitting at a light with my foot on the gas. Haven't seen this recently after replacing the vacuum hose though but the random shifting has been on again off again since getting the transmission replaced and it was not there before hand.

Any insight would be most appreciated thanks