Modulator is on the side of the tranny, outside, has a vac line to it.
It is possible to adjust it for snappier shifts, but this will only hide the problem, not fix it.
Steve Brotherton has a long article about transmission adjustments. The link is in an old thread, but I don't remember which now. I'd read that before jumping around too much, then you will know what to tell the shop.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!