interesting info i found on a different site;
"At full throttle my turbo 400 upshifts at 4,500 rpm. I want it to upshift at at least 5,000, maybe even 5,500. I know that the modulator controls upshifts, but only up to WOT I think. After that, the springs in the Governor decide when to upshift right?
So should I get different springs for the governor or adjust the modulator? If I adjust the modulator won't all upshifts be higher up in the rpm range? I mean, If say I adjust it to 5,500 WOT upshift, won't my partial/cruising throttle upshifts also be up much higher?
Your understanding of the modulator and governor operations is incorrect.
The governor weights and springs work together
The springs in the governor control shift points primarily at light throttle. Changes to the springs affect shift points more up to 35 mph area depending on gear ratio - tires ,etc.
The weights affect higher speed shift points more than the springs do.
Later WOT shift = higher RPM will happen by lightening the weights ( inner) on the governor.
The vacuum modulator affects mostly th e light throttle shift points. At WOT the vacuum will be near zero and the modulator will be ineffective. This will have main line pressure raised.
I would suggest you purchase a kit with different weights and springs to modify your governor. Or simply start grinding on the inner weights for later WOT shift points.
The lighter weights will affect light throttle shifts slightly on the t-400 trans , but mostly the higher speed shift points"