Transmission shifting

I have a 1995, Chevy 4x4, 4160e trans, my
son was driving it down the road and hit a pot
hole in the road and it bounced the truck, from
then on it shifts fine then out of the blue it will
down shift on its own, all the gears are strong,
but will not up shift, unless you pull over and
take off again, I’m lost don’t know what to try