904 slow shifting into high gear????? Help plz!

Since you changed all the other parts there's not much left but those 15 year old seals. When you take the valve body out look and see if it has a restrictor driven into the case port for the front clutch feed. Maybe someone had a shift kit in it before (many shift kits use a restrictor in the front clutch feed port) and it's not supposed to be there for the manual VB. That would slow down the fluid flow to the front clutch pack possibly causing the soft shift.

The slow engaging into gear when cold is common with a Mopar and is generally no sign of a problem. Most Mopars do it cause the converter drains back when it sits due to the manual valve exhausting in park. I always start mine in neutral to fill the converter up faster. Remember no fluid flows in park on a Mopar unless it has been modified.