What is it? And what does it entail? Expensive? Please make me understand?

 

The refwerence to a Valve body is the working hydraulic brains of an auto trans.
Ashift kit modifys the pressure and shift poits/firmness.
A complete VB from a trans shop-performance wise- is also tested after being modified. This makes it mostly a bolt in.
This is a nice improvement to even stock trucks. You will feel it shift gears. The only way to avoid feeling an auto trans shift is to slip the clutch packs. This creates wear on them.