Why does your 1998 silverado start shifting hard after long periods of driving at speed over 45 until you shut off and start back up again?

Why does your 1998 silverado start shifting hard after long periods of driving at speed over 45 until you shut off and start back up again?
Sounds like a bad solenoid. But if it shifts hard from first to second then from second to third but fine when from third to over drive forth but then shifts a little hard when down shifting through the gears if that is the case might need to change transmission filter and fluid sometimes overfilling the transmission with fluid could do this as well.