904 adjustment?

Part of the problem with manual shifting is that the TP is usually not at full when you shift causing some delay due to the pressures being lower.
Try stepping into it farther just as you shift it and see if that helps.

Blocking the accumulator helps with that as does opening up the oil holes in the separator plate in the valve body to allow the fluid to get to the clutches and bands faster.

Try stepping into it like I said, and see what the results are.

Of course a stage 2 shift kit will fix that also. :D