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2009 Acadia SLT, 180,000 Km
Looking for tips of where to start to solve this. I'll try to leave all relevant information:

Noticeable surging once at speed and driving normally, RPMs bouncing slightly at ~1500 RPM. Seems like transmission likes to shift down if I try to accelerate gently as it has trouble in the 1500/1800 RPM range. After the shift down it accelerates fine.
Harder acceleration seems fine, good power.
Idle seems fine, stable at normal RPM
Plugs and coils all replaced 3 or 4 years ago as I had much worse surging/bouncing RPMs, but was obvious trouble with coils, has always been perfect until now.
New engine code, cylinder misfire, P0300
Rear cat. converter failed long ago and in the summer clogged the exhaust and is currently not installed.(Always has a code).
New transmission installed in ~2017 before I purchased the vehicle.

Hoping this is something easy like air/fuel filter or o2 sensor!
Thanks for any help.
 

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2009 Acadia SLT, 180,000 Km
Looking for tips of where to start to solve this. I'll try to leave all relevant information:

Noticeable surging once at speed and driving normally, RPMs bouncing slightly at ~1500 RPM. Seems like transmission likes to shift down if I try to accelerate gently as it has trouble in the 1500/1800 RPM range. After the shift down it accelerates fine.
Harder acceleration seems fine, good power.
Idle seems fine, stable at normal RPM
Plugs and coils all replaced 3 or 4 years ago as I had much worse surging/bouncing RPMs, but was obvious trouble with coils, has always been perfect until now.
New engine code, cylinder misfire, P0300
Rear cat. converter failed long ago and in the summer clogged the exhaust and is currently not installed.(Always has a code).
New transmission installed in ~2017 before I purchased the vehicle.

Hoping this is something easy like air/fuel filter or o2 sensor!
Thanks for any help.
I have a 2018 with the same problem. It’s been to the dealer three times, going for a fourth( new dealer) this week. Suspects are transmission, throttle position sensor, throttle itself.
 

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I have had this issue with my 2013, though I also had multiple other issues at the same time so not entirely sure which "fix" fixed it. I'll just list a few leaders. First off, check or just go ahead and replace the gas peddle/sensor. Mine had developed an almost dead spot at a certain position. Would randomly send a not-nominal signal which confused the throttle control. The other fix I had to put in was replacing/servicing the transmission. I used mine for occasional heavy towing, so I knew that was going to be a need-to-service item down the road.
I did to coils, plugs and injectors at one point, but that cured random cylinder cutout, had nothing to do with surging.

Hope these help!
 

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Mine is currently in the shop,again. So far they replaced the torque converter. But they see another anomaly happening. In the day of the road test, the tech saw a split second fluctuation in the throttle signal as I touched the gas pedal. A 5% flux, which is a lot. We may have a bad throttle. They still have the car….
 
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