My car will surge all in a sudden on its own while I am driving. It started in the last few days, and I was not even giving gas when that happened. It seems like the tranmission is slipping, and the tach will surge upward to 6,000 rpm. I am thinking if it is the transmission, it will most likely to happen as you apply gas, but it happened while the car was in steady speed. Then something caught and all was normal. Any idea if it may be my tranny just about to go? It is my '87 300E. If it is not the tranny, what may be the cause and what should I do?

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95 R129
04 Infiniti G35.5 BS
10 X204