Downshifting into 1st?
Why not just come to a complete stop?
You should never be downshifting into 1st unless it's from a dead stop.
Otherwise, it is a recipe for disaster.
Ask me how I know?
1st gear paddle downshift @ 30mph into WOT w/ 13 psi blowing the tires off.
Stock 80k trans started slipping a week later.