You can try to give the modulator on the side of the transmission a click or two to see if that helps. I forget if CW or CCW tightens shifts. There's a disk about 2" across just aft of the driver side of the bell housing. In the center is a rubber cap about 1/2" across. Remove the cap to expose a plastic bar sitting across low points in the exposed minaret (well, what would you call it?). Pull the bar (it's actually the top of a T) out just enough to clear the minaret. Move it one position then push it back into the minaret. Replace the rubber cap and go for a drive. I wouldn't move it more than a half turn total. If it needs more than that... the tranny needs more than an adjustment.

The proper way to set the modulator is with pressure gauges and a bigger brain than I have.

This will buy a little to a lot more time but start saving pennies towards a rebuild.

Sixto
87 300D