About your only hope is that you are low on fluid or too much vacuum is getting to the modulator. If you wish to test that pull the line to the trans off its connection under the hood. It should then shift very harshly. If it makes no difference and the fluid level is right, it gets worse.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician