The next time this is going to occur, tap the brake pedal lightly with your left foot, or hold that pedal down just a little. If that makes the problem not occur, you are feeling a shudder from the torque converter. The clue is the speed you listed. At lower speeds it is not trying to lock up yet, (for better fuel mileage). At higher speeds it locks up solidly. At mid speeds, it is starting to lock up, but it engages slowly so you do not feel a sudden thump. It is supposed to slip and gradually becomes fully locked. The shudder is almost always caused by using the wrong transmission fluid. A fluid and filer change will solve that.
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Sunday, July 2nd, 2017 AT 9:56 PM