The gov only changes when it shifts, not how firm necessarily.
The oil flow through the separator plate in the valve body is where you need to slow the oil flow so engagements are softer.
Those oil ports are often drilled larger to allow fast apply of bands and clutches, so you may actually want to swap your valve body to someone who wants the firmer shifts.
Of course there are other ways of doing it, but it would require a lot more work and disassembly of the valve body.
I have seen valve bodies with small cotter pins in those drilled holes to slow the fluid and therefore slow the apply when someone over drilled them.
If it were me I would leave or change the pressure to what it should be, and deal with what makes it too firm.
If you lower the line pressure you will be lowering the holding pressures of the bands and clutches also, and that could cause damage from slipping under load.
It will also make your shifts way late, because lowering the pressure causes the shift valve springs to need more pressure to move and therefore it waits until the governor can't resist it any longer so you basically end up with the same problem because you would lower the TP to try and compensate for the late shifts and in turn lessen the holding power even more, but still have a high fluid flow causing it to still be harsh in shifting.
Raising line pressure will cause it to shift early for the same reason on the shift springs, but it would still be harsh from the lack of the accumulator spring, and still having oil flowing to the bands and clutches at a raised rate (still harsh) because of the drilled holes in the separator plate and having to raise the TP to make them later again after raising the line pressure.
This is what AJ was saying about the pressures being opposed by other pressures.
I really feel you need to slow the apply by limiting the flow to the clutches and bands, and put an accumulator spring back in it.
Either that or swap back to a more stock valve body and spring and let the younger guys have the real firm shifts. (a lot less work) to get what you want.
Now, if you swap valve bodies you will need to take a good look for and remove any orifice plugs that may have been put in the case due to the shift kit instructions, and will if there are any they need to be removed when going back to a more stock valve body. (easy enough by screwing a deck screw into them and pulling them out)
JMO