My 84 300d runs great but doesnt shift properly. The main problem is down shifting. When the accelerator is floored the trans stays in high gear (3rd or 4th depending). If I change gears with the selector everything works normally. Also it seems like it doesnt hold the gears long enough and I end up in 4th way too soon.

Things I have checked so far:

Vacuum: All lines are good and routed to the correct places. I replaced all the soft rubber pieces I could see and checked all the plastic lines with my mity vac.

IP "full load" linkage: Adjusted to be fully open when accelerator is pushed to WOT

ALDA: Removed and cleaned both banjo fittings, adjusted the screw which still had the original cap on it. Turned 3/4 turn CCW.This seemed to soften shifts and increase power, but caused slipping from a dead stop after the trans is hot, unless "L" is selected on the shifter. Turned it back 1/4 and seems to be ok but have not road tested extensively.

So my hunch is one or all of the vacuum modulators are inop. Do they go bad often? Is the ALDA modulator normally open.. meaning when voltage is sent to the modulator should it close or open? This one is open with no power. I havent tapped power into it to see if it closes. What sends the voltage signal to the modulator? Is there a control unit? What sensors control this signal?

Thanks in advance!