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Hello, I'm hoping to get some help for an issue I'm having. I bought a 2003 honda civic, about a week after getting it started to notice a jerk whenever I would press or let off the gas pedal. Sometimes it's barely noticeable and other times it's a significant jolt, and not all the time just at random after I've been driving for a while, sometimes it's accompanied by a very low thunk sound.

I took it to multiple mechanics who said they couldn't reproduce it with one saying it wasn't going to 4th gear so they suggested I go to a transmission shop. They said it was slipping and I paid almost what I paid for the car to have it rebuilt only that issue remained, I've taken it back to them multiple times and even once left it there for a whole month. They have taken the whole trans out and worked on it 4 times and say it's good to go but it returns. I suspect it's not the transmission at all as it's done it across the original and 2 rebuilt ones. I've been driving the car with this issue for months and haven't noticed any other problems. Any help would be appreciated, Thank you.