I have used IH tractors with TA since 1964 and the dealer people said move the lever quick so that is how we always do it. Maybe not as fast as an electronic shift but not sliding it in.
On the 966, it feels like the engine releases briefly and then grabs normal, not a violent grab. It is the hesitation I am concerned with. I checked the pressure last spring out of curosity and it was good. Tractor has not had much use and no load on it since spring. I have not had a MCV apart. Any cautions or tips?