If just one gear in an automatic transmission blows, they usually insist on replacing the entire transmission because the parts need to wear evenly or something. Sorry :/

My friend's car was having similar problems to yours and it also wound up being a chip. I think it was the speed sensor. Basically, the car didn't know how fast it was going, so it couldn't shift into the proper gear.

When my clutch (manual transmission thank god) fell apart, it had issues accelerating in every gear, shifting was really "soft" and eventually the car just refused to move.

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