[Tom Goldman]

is that a typo, .5 to .75 and not .05 to .075?
All TH400 valvebodies that use the modulator valve are notoriously slow and can be effected by a binding release valve.
If you are serious about racing on a Pro tree with a 400 , or even just being consistant on the full tree , the Griner brake is the ONLY choice.
I've used and sold them for at least 25 years and there is none better.
Plus the normal 4-500 RPM lag on the 1-2 shift is gone ,the shift is instant.