If you hear it or feel it click then immediatly shift, I'd suspect the shift rod bushing on the transmission. Quick way to check is to push the shifter a little bit past D -- if it works immediatly, the bushing is gone. The click is when the tranny lever moves to the detent, it's not being pushed all the way into the correct position by the linkage, and won't upshift until the lever moves the rest of the way by itself.
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!