This is a trait of 400's known as "blow shift". Basically, it is a fail-safe from the engine grenading itself. It is not an option, but a safety mechanism for the engine and trans. In fact, it can be seen in 700-4R's too. I was driving a buddy's 427 4x4 truck with a 700 in it, and just put it to the mat until the trans upshifted. Blow-shift is the "trans guy" term. Still cool tho ......
