my 1991 190e 2.3 shifts hard i am going to do a trans service but if that doesnt do it should i replace the modulator or any ideas?? it has 103000 miles

 

What's your vacuum pressure to the modulator?
If it's like 5, do as suggested above.
If you have good vacuum pressure, 10-13 ish, check to see if the modulator valve holds pressure.
If not, replace it and see how you do.
Good Luck and WELCOME to the forum.