1983 300d 722 transmission won't downshift, transplant into dodge dakota

[74Dusted]

Okay, right from the get go, here's the basics.

I have an OM617 and 722.3 (i believe it's the 722.3? 4-Speed) from an '83 or '84 300D transplanted into my '92 Dodge Dakota with an All Wheel Drive conversion. She's been running perfectly for almost 2 years.

This problem popped up, with no warning. I literally drove the truck to the store to get snacks, and when I drove home, it would no longer downshift by itself based on throttle position. At the same time it developed a Rapid Upshift problem where it will shift through all of the gears and it's in 4th before it even hits 15mph

It starts out in 1st gear, rapidly upshifts, and then refuses to downshift no matter how much you mash the throttle. It will downshift to 1st (by itself) if I come to a complete stop, or I can manually downshift it.

My first thought, was that the Kickdown / Bowden Cable had snapped, but it's intact and functioning (even tried adjusting it, thinking maybe it stretched some). Fluid level is correct and the fluid is clean. Transmission isn't slipping either and it averages 165 degrees fully warmed up and driving (I have a Trans Temp Gauge installed in the truck)

I'm kind of lost here, considering that whatever happened, happened without warning.