So a fresh battery completely solved the surging & bucking? What caused you to finally replace the battery? Was it cranking slowly?
Sorry in advance for the lengthy reply...
I had ran out of all other options, I knew it wasn't the alternator because my boyfriends had alternator issues when we first got his mazda 3 and mine was doing none of the things his had done. Dealer also tested and verified it was running fine. I went over every detail of the car and all my issues in the past and remembered back in 2017 when I got caught in a hail storm the body shop killed my battery and told me they replaced it. Well I have a cover on mine so I never took it off to check anything because I was afraid to disconnect the terminals in the wrong order. I had help changing it safely thanks to youtube, when I fully removed the battery and took the cover off the entire underside of the battery and tray had dried acid on it. My battery was leaking from somewhere, none of the terminals are gunky AND it was the original battery from when I bought the car in 2014! The body shop 'replaced' it but the rep at Mazda said it was old and showed me the stamp.
I have since noticed my car starts right away, no drawn out igniting, I all around feel like I have power again. I can climb an on ramp like it used to, no delay in accelerator response I touch the gas and feel it instantly. Dome lights are brighter at night, my shifting in automatic is smooth like butter, manual/sport mode feels more aggressive again if that makes sense. I can crawl steadily uphill into my driveway and not feel like i'm choking it to death. Even my coasting with feet flat on the floor is smooth again. My adaptive headlights are more responsive now, I turned them off when this all started because it was terrible on hard corners at night. No more low idle and rpm drops just sitting at a light.
I'm not aggressive on my baby but I drive it and know that I can remove myself from a dangerous situation on the road if I need to and for a long while I was worried without the power under me to do it.