You have a 722.x tranny with a modulator.
You will need to find the vac line to the modulator and check the rubber connector on both ends. Get a MitiVac hand pump if you don't have one and check to see that the modulator and line hold pressure, and what sorr of vac you have on the manifold or control valve (don't remember at the moment if this is a gas or diesel engine).
Once you have established vac integrity and proper vac signal, you can start with the adjustments. See some other posts on this subject, Steve Brotherton has a very nice page (or refers to one, anyway) describing the various adjustments. The link does a much better job than I can of describing what to do.
I suspect an adjustment problem rather than something serious.
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!