It will what seems like go to first gear whether at 65 or stopped?

At any time two weeks two day a month. It will what seems like go to first gear whether at 65 or stopped. Turn key off every things just find for a while again. Any one I ask doesn't know what is wrong. Seem to me which I am not a car guy but is this a electronic thing or what? At shop wants $750.00 to repair a lot of stuff but I am not sure if he is just given me a work over.