Speedometer issue or ...?

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Hi. My tempo recently had a wiggly speedometer needle and then a few days later while driving the dial went to zero, stayed at zero and the car was stuck in first gear and wouldn't shift out of first. I looked at all the cabling and everything looked good to me but the problem remained so I took it to a transmission shop and he said everything looked good but it was missing a grommet which he replaced. We picked up the car yesterday and experienced the same problem again. when the car heats up, say after going 5 or 6 miles the speedometer hits zero and won't shift out of first. Anyone have any clue what could be the cause and how expensive it is to repair? Thank you