Is the engine taking a lot of throttle to take off with?
What everyone calls the KD mechanism, is actually a throttle-pressure adjuster, with the KD being a function of that. But think of that mechanism as firstly being the throttle pressure adjuster.
So as the throttle is opened, it pushes the slotted member rearwards increasing the throttle pressure at the trans. This does two things, it fights the governor as to when the shift will occur, delaying the roadspeed at which the trans will shift. And since the pressure is higher, the shift will be harsher.
Ok, so if the engine is down on power, you will naturally drive deeper into the carb, using more than normal throttle. and so I repeat; Is the engine taking a lot of throttle to take off with?
The why of the engine being down on power is another matter, from as simple as needing a tune-up, to a frozen stator in the convertor, to not running on all cylinders.
In reverse, all pressure regulation is bypassed, and the L/R servo gets whatever the pump can put out which can max out ~275 psi.
If the throttle pressure valve is being adjusted by the KD mechanism, the pressure will be higher than normal, which being maybe 90psi. By lengthening the KD rod, you increase the Part Throttle pressure. Bad idea. Especially if that now limits your throttle opening. And this is what
@CudaFactHackJob is trying to get you to understand.
Now, you keep thinking the car is all original, but if the rear end has been swapped to one with a higher Torque Multiplication, then it will spin the driveshaft up faster, commanding an earlier shift. This calls for a reduction in throttle pressure to prevent delayed harsh upshifts. Or a reduction in governor pressure to get back on track.
So you could have multiple issues.
I recommend a compression test, and to at least set the timing after proving the balancer mark; to see if you even have an engine. And then a stall test.
And finally, figure out your rear gear ratio, and compare it to what it came from the factory with, if you can. Alternatively, figure out if the trans in there is what it left the factory with, if you can.
But I repeat; Is the engine taking a lot of throttle to take off with? This could be a sign of a bad TC.
