You should see if the line to the modulator is tight. Very difficult at the bottom. Try and trace it at the top and suck on the line. Watch out for oil. If there is oil or the line doesn't hold a vacuum then this is the problem.
There is very little that can be done externally to change the relative shift strength gear versus gear. It can be made softer for all or harder for all at the modulator. Some times a combination of shift timing (done with the control pressure cable) and modulator adjustments can smoose over the rough spots.
And be sure that he motor is running at appropriate power. A motor that is lugging will shift harder, due to the lowered manifold vacuum.
Bosch Master, ASE Master, L1
33 years MB technician