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.