I had a 2015 Silverado I…
I had a 2015 Silverado I think it had a 6 spd same issue it would shudder then down shift going up a hill then going downhill it would downshift the only positive aspect of the truck it did ride like a Cadillac and it was totally loaded as far as the trans flush as the post states you never do a trans flush unless your going to eventually rebuild it you push all those partials thru the vains and passages of the valve body. Also I did sell my truck it was a headache with the trans that I didn't want to deal with