Hmm before I did your pressure spring and a modified converter flow valve all of my shifts were smooth as butter under WOT. Went 2 years like that. Now after those hydraulic mods my 3-4 is pretty firm only under WOT. All others still feel like they used to. Why would higher pressure and zero knockdown do that? Is it because the clutches are grabbing alot harder now which makes you feel this supposed tie up? Can only feel it if the converter is locked and can't feel it at all if part throttle driving.
