The warmer the fluid gets the thinner it gets.
Thinner fluid gets by valves and such in more volume which causes the pressure that is supposed to move valves and such to be lower.
My trans is adjusted to be the way I want it to work when it's fully warmed up, and I really don't like driving it until it is all the way warmed up.
(the cold fluid makes my shifts too early because of less leak by in the pathways causing the pressure to be higher and moving the valves sooner.)
