904 shifting problems

What rpm does it shift at? My first guess is you need a higher rpm governor weight package and/or a different set of 1-2 and 2-3 shift valve springs.

The screw your referring to is the throttle pressure valve idle setting. It does not affect the rpm at which the trans. shifts at wide open throttle. Only affects the shift rpm at light throttle.

What do you mean by it's "stacking gears"?

BTW: I quit using B&M kits a long time ago cause some of them didn't work right. Very unpredictable.You may put in 3 or 4 and they work right and then put in the next one exactly the same way as the others and it not shift right. I only use Trans-go kits now.