i have the same problem and they said that it could be that the stumble could have always been there but with the chip that i notice it more. They said that the chip would magnify an ignition problem if I had one, but seriosly if they fix it let me know. It's annoying somethings. But i did the same stuff you did except for cleanning the contacts again. If the chip wasn't making a good connection then it wouldn't be working. It's that simple.
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